Image copyright AFP Image caption The rioters are negotiating with officials to end the protest 
 
 Police in Brazil say rioters in a jail in the southern city of Cascavel have killed four fellow inmates and injured several others. 
 
 Two of the victims were decapitated while two more died after they were pushed off the roof of the building. 
 
 The authorities restarted negotiations with the rioters on Monday morning in the hope of ending the stand-off. 
 
 At least 700 prisoners are reported to be involved in the uprising, which began on Sunday morning. 
 
 The prisoners are said to be unhappy about how the prison is run, as well as about food and hygiene there. 
 
 Local media showed prisoners beating men held with ropes around their necks on the roof of one of the buildings. 
 
 'Psychological torture' 
 
 The trouble broke out when warders delivering coffee to inmates were reportedly overpowered. 
 
 As many as 1,000 prisoners then took over parts of the jail, ransacking and setting fire to much of it. 
 
 The BBC's Wyre Davies in Rio de Janeiro says that rival prison gangs are most likely taking advantage of the riot to settle scores. 
 
 The leaders of the rebellion are holding at least two prison guards hostage. It is not clear whether the hostages have been harmed. 
 
 Guards have not yet been able to retrieve the bodies of the four people killed in the unrest. 
 
 "They are using the severed head of one of the prisoners to inflict psychological torture on one of the hostages," said Jairo Ferreira, lawyer for the prison agents' union. 
 
 "There are scenes of terror inside the jail now," he told local newspaper Gazeta do Povo. 
 
 Negotiations restarted first thing on Monday to put an end to the uprising, which has led to the destruction of most of the penitentiary, according to O Globo newspaper. 
 
 The Security Secretary of Parana State, Maria Tereza Uille Gomes, has travelled to Cascavel to take over the negotiations. 
 
 Brazil has the world's fourth largest prison population, with half a million inmates in facilities meant to hold 300,000. 
 
 Our correspondent says that, across the country, many poorly resourced jails are in effect run by powerful crime gangs. 
 
 Earlier this year the UN High Commissioner for Human Rights, Navi Pillay, called for an investigation into the high number of violent deaths in Brazil's prisons after previous riots at a jail in the north of the country left dozens of people dead. ||||| Brazilian authorities reached a deal with rioting prisoners Monday who killed four fellow inmates, beheading two of them, and held two guards hostage. 
 
 Elson Faxina, a spokesman for the Parana state attorney's office, said an agreement was signed to end the uprising at the Cascavel city correctional facility and that prisoners were currently being transferred to another jail. 
 
 "After that, the two guards who were held hostage will be freed," Faxina said, adding that police still had to enter the jail to assess the damage and determine if there are more victims. 
 
 Some 800 inmates -- or 80 percent of those being held at the facility -- took part in the revolt, he said. 
 
 The riot erupted Sunday as breakfast was being served, with inmates overpowering guards. 
 
 Two prisoners were beheaded in the first surge of violence, and two others were thrown off the top of the cellblocks. 
 
 View gallery Screen grab taken from CGN shows inmates holding a hostage at a prison in the southern city of Casca … 
 
 The guards were taken hostage in the melee. 
 
 An official with the guards' union said only 10 wardens were on duty at the time. 
 
 Prison authorities said the inmates were demanding improved facilities, better quality food and more flexible visiting hours. 
 
 But the inmate-on-inmate violence also suggested that rivalries between competing prison gangs played a role in the uprising. 
 
 "The fact that prisoners took hostages would reinforce that view," Faxina said earlier. 
 
 View gallery Screengrab from CGN shows inmates taking hostages at a prison in the southern city of Cascavel, Para … 
 
 Television images had shown some of the rioting inmates -- dressed in orange jumpsuits with their faces obscured -- on the roof of the facility during the mutiny. 
 
 Police have yet to identify the four inmates who were killed and retrieve the remains of the two who were beheaded, according to authorities. 
 
 - Prison overcrowding - 
 
 The state correctional center, which houses 1,140 inmates, has a capacity for 1,181, according to official data. 
 
 Anthony Johnson, president of the prison guard union in Parana state, said the true capacity of the facility was just 900. 
 
 "So there's overcrowding," he said. "For us, the situation is tense now but we hope it is resolved. A jail of this kind needs investment." 
 
 According to the union of prison workers, a major lack of investment plagues the system, and the facility was threatened by a scarcity of operational and technical professionals as well as proper maintenance. 
 
 "Many times the workers have to invest their money to buy the necessary items to do their jobs," the union said in a statement. 
 
 "Without investment, we are always exposed to this. The prisoners claim that food is bad, that there are no lawyers to process things, minimal hygiene products don't exist, there are few correctional officers. All the factors together are a tragedy waiting to happen." 
 
 Brazil holds 548,000 inmates in its prisons, but needs 207,000 more spaces to avoid overcrowding, according to the NGO Conectas Human Rights. ||||| Image copyright AFP Image caption "Tornado" officers brought in to stop the riot have been seen outside the prison covered in paint 
 
 Up to 240 prisoners are being moved out of HMP Birmingham following a 12-hour riot at the jail. 
 
 Inmates took over four wings, started fires and gained access to medical supplies as they rampaged in the prison. One man was taken to hospital. 
 
 Friday's disturbance has been described by the Prison Officers' Association as the worst since the Strangeways jail riot 26 years ago. 
 
 Justice Secretary Liz Truss said there would be a "thorough investigation". 
 
 Rioters would "face the full force of the law," she added. 
 
 UK prisons chief Michael Spurr said there were "serious problems" in jails that would not be solved immediately. 
 
 Image copyright AFP/Getty Image caption Specialist teams have been leaving the prison on Saturday 
 
 The Ministry of Justice said riot teams restored order to all four wings of HMP Birmingham just after 22:30 on Friday. 
 
 The disorder was understood to have involved up to 600 inmates. 
 
 Two wings suffered "superficial damage" with more serious damage caused to two others. 
 
 G4S is in control of the jail and the cost of the damage will be borne by the firm, the BBC understands. 
 
 "Our teams have worked tirelessly throughout the night to assess the damage caused, start the process of clearing up and capture any evidence that could be used by West Midlands Police for any subsequent prosecutions," a G4S spokesman said. 
 
 "This disturbance is rightly subject to a thorough investigation and we are working openly and transparently with the Prison Service and other relevant authorities to understand the causes behind it." 
 
 Image copyright AFP/Getty Image caption Groups of prisoners are being moved from HMP Birmingham to other jails around England 
 
 The Ministry of Justice said: "The prison remains calm and ordered with additional staff on site to offer support. 
 
 A "limited regime" is being offered to inmates not involved in the disturbance, the spokesman added. 
 
 Prison visits have also now resumed. 
 
 Image copyright Reuters Image caption Riot teams were deployed to tackle the disorder 
 
 Mike Rolfe, national chairman of the Prison Officers' Association, said more than 30 staff had left the Winson Green prison in recent weeks. He compared the trouble to the notorious Strangeways riot in 1990. 
 
 "We've been warning for a long time about the crisis in prisons and what we are seeing at Birmingham is not unique to Birmingham, but it certainly would seem that this is the most recent worst incident since the 1990 Strangeways riot," he said. 
 
 Ms Truss said: "I want to pay tribute to the bravery and dedication of the prison officers who resolved this disturbance. 
 
 "This was a serious situation and a thorough investigation will now be carried out. 
 
 "Violence in our prisons will not be tolerated and those responsible will face the full force of the law." 
 
 Image copyright @snappersk Image caption Members of the specialist Tornado squad left the prison on Friday night 
 
 Image copyright PA 
 
 Analysis: BBC Home Affairs Correspondent Danny Shaw 
 
 As the investigation and clear-up operation get under way at Birmingham Prison, the immediate concern for officials will be the risk of "copycat" disturbances. 
 
 Many jails are volatile places, with violence never far from the surface. 
 
 Reports of the rioting and rumours about how it all began could encourage others: it may be no coincidence that this is the third serious prison disturbance in six weeks after Lewes and Bedford. 
 
 The other main consequence of the damage is that it'll put a number of cells out of use at a time when capacity is already stretched. 
 
 Last week, there were around 1,200 spare prison places across England and Wales - that may seem like a lot but, spread across a large geographical area with different categories of prisoner to accommodate, it doesn't leave much slack in the system. 
 
 The BBC understands that one prisoner was hurt during the riot and taken to hospital with a fractured jaw and broken eye socket. 
 
 Prison wings are now being inspected to assess the full scale of the damage after prisoners took control of the category B prison on Friday morning. 
 
 Rodger Lawrence, chairman of the Birmingham Prison Independent Monitoring Board, said his members had not seen anything of concern during a visit earlier this week, but said the riot "didn't come as a complete shock" as there had been "a build-up of frustration" over prison conditions. 
 
 Image caption New toilets were among items seen being driven into the prison on Saturday 
 
 Michael Spurr, who is chief executive of the National Offender Management Service Agency, said overcrowding, reduced staffing and drugs had put pressure on prisons. 
 
 "On a day-by-day basis governors and staff keep prisons safe and manage a very difficult population extremely well," he told BBC News. 
 
 "Yes, there are assaults, there is too much violence, but we are tackling that. 
 
 "It will take some time but events in prisons such as yesterday do happen on occasions." 
 
 He said a £1.3bn investment in new prisons over the next five years, which includes plans for more prison officers, drug tests for inmates on entry and exit from prisons, and more autonomy for governors, would help tackle the issues. 
 
 "Over the coming months and years, we will turn it around," he said. 
 
 Image caption Another unverified photo circulated online purporting to show scenes from inside the prison 
 
 Trouble flared after an officer was "rushed" by inmates at about 09:00 on Friday. 
 
 Violence quickly escalated and due to the scale of the disturbances the Prison Service took over the incident and specialist Tornado units were deployed to regain control. 
 
 Prison units from across the country were also drafted in to assist. 
 
 Image caption An unverified photo appears to show debris and damage caused during the disturbance 
 
 During the disturbance, the BBC was contacted by several men claiming to be prisoners at the jail, who said poor conditions were behind the disturbance. 
 
 The men, who said they were calling from inside HMP Birmingham, cited inadequate staff numbers, poor healthcare and nutrition. 
 
 They said being on "lockdown" in their cells all day was a major factor that contributed to the trouble. 
 
 HMP Ashwell riot 
 
 BBC Home Affairs correspondent Danny Shaw believes that although the riot at HMP Birmingham was "clearly very serious", it may not be the worst since Strangeways, as the Prison Officers' Association has claimed. 
 
 He said: "In April 2009, there was a riot at Ashwell prison in Rutland involving 400 inmates. 
 
 "It caused such extensive damage to three wings in the old part of the jail, the entire prison closed permanently in January 2011 because the cost of repairs would have been too great."
– Two prisoners were beheaded and at least another one died after being thrown off the roof in a riot that erupted yesterday in a prison in southern Brazil, authorities say. Inmates of the penitentiary in the city of Cascavel took at least two agents and several other inmates hostage in the uprising, said military police Capt. Ricardo Pinto, who added that negotiations for better conditions in the prison were still under way last night. The BBC and AFP say the riot was still ongoing this morning, and that a fourth prisoner had been killed after also being pushed from the roof. The revolt began before sunrise yesterday when a prison guard was captured during breakfast. Prisoners set some objects on fire and were using metal poles to cause damage to the 928-bed prison that housed more than 1,000 inmates. Dozens of the prisoners climbed onto the building's rooftop, with their faces covered with white fabric. Local media images showed at least 30 rebellious inmates shouting while they beat men held with ropes around their necks, or whose hands were tied behind them. The rioting inmates waved banners emblazoned with the initials PCC for a criminal prison gang formed in the 1990s. Jairo Ferreira, a lawyer for the prison guards' union, said the prisoners rioted to demand better food and medical care.