(CNN) -- Syrian government forces killed about 10 people Thursday in the besieged western city of Homs, according to a statement from the Local Coordination Committees of Syria, an affiliation of groups that organizes and reports on protests in Syria.
In the Bab Sbaa neighborhood near the center of Homs, shooting continued for hours before tapering off, the statement said. Communications lines were cut in many places and it was not possible to deliver medical aid to the wounded, the LCC said in its statement.
Workers in a number of cities and villages -- including Idlib, Daraa, Daeel and Hama -- went on labor strikes Thursday in support of the people of Homs, the statement said.
A witness in Bab Sbaa said government thugs were roaming side streets of Homs, setting houses afire and firing aimlessly to scare residents. Tanks were knocking down balconies, destroying shops and firing indiscriminately, he said.
He said other witnesses reported gunfire from a government checkpoint in the al Qasr district; in the al Waer region, witnesses reported hearing explosions and gunfire coming from the military college.
In the Al Hamraa region, residents reported sniper fire coming from towers.
Demonstrations occurred in Damascus, but were cut short by a heavy security presence, the LCC statement said.
Tension and violence between security forces and demonstrators have plagued Homs for days.
In Washington, White House Press Secretary Jay Carney condemned the attacks.
"We call on the Syrian regime to cease the violence," he told reporters. "We are working with our partners internationally to put pressure on the Syrian regime to get it to cease and we believe that it is clear now that (President Bashar al-Assad) has given up the opportunity to lead the transition that the Syrian people demand and he has lost legitimacy by doing so."
On Wednesday, Human Rights Watch said Syrian security forces have intensified their campaign of mass arrests in cities that have had anti-government protests.
The cities include Hama, Homs, and suburbs around Damascus, the group said.
Citing "reliable activists and witnesses," it estimated that security forces have arrested more than 2,000 anti-government protesters, medical professionals caring for wounded protesters and people alleged to have given information to international news media and human rights organizations.
"President Assad talks reform but continues to practice repression, not only through the widespread killings of demonstrators but also through mass arrests," said Sarah Leah Whitson, Middle East director at Human Rights Watch.
The LCC Local Coordination Committees, an affiliation of groups that organizes and reports on protests in Syria, estimates that more than 15,000 people arrested since the beginning of the protests remain in detention, HRW said.
"Human Rights Watch has already documented widespread torture from the accounts of people who have been released, causing concern that many detainees still in detention are being tortured," the group said.
Independent accounts of the situation in Syria are hard to come by; most of the international media have been barred from the country.
The unrest in Syria began in mid-March after teens were arrested for writing anti-government graffiti in the southern city of Daraa, according to Amnesty International.
As the clashes intensified, demonstrators changed their demands, from calls for freedom and an end to abuses by the security forces to calls for the regime's overthrow.