(CNN) -- Syria's major opposition group condemned Bashar al-Assad's regime Wednesday for "brutal massacres" this week and urged the U.N. Security Council to protect civilians against "acts of genocide."





"The regime is using children as human shields so that tanks and armored vehicles can storm residential areas," said the Syrian National Council, which said that about 250 people have died over a 48-hour period.





"Incidents of gruesome murders have been recorded," the council said Wednesday, including the killings of four brothers and the beheading of a sheikh, whose head was hung above a mosque entrance. Both incidents occurred in Idlib, and the council says "acts of genocide" are occurring in Zawiyah Mountain in Idlib province in the northwest and the city of Homs in the west.





It cites "the regime's use of heavy weapons and artillery in shelling civilian neighborhoods, as was the case in the Baba Amr neighborhood of Homs, as well as in the villages of Kansafra, Kafar Awaid, and Mazrain, where a large number of residents were killed. Other residents were forced to flee under heavy gunfire," the council said. The villages are in Idlib province.





The violence spiked as Syria agreed to an Arab League observer mission Monday aimed at ending the violence between regime forces and protesters that started in mid-March. The United Nations this month estimated that about 5,000 people have died in the bloodshed.





"The SNC directed letters to representatives of the 15 member nations of the U.N. Security Council, including the permanent members, urging them to convene in an emergency session to discuss the brutal and systematic killings, the humanitarian situation, and the displacements forced by the regime and its security and military apparatus," the group said in a news release.





The council also sent "urgent communiques" about the violence to the Arab League; the Organization of Islamic Cooperation; the Gulf Cooperation Council; the General Secretariat of the United Nations; the U.S. Department of State; the British Ministry of Foreign Affairs; representatives from the Chinese Foreign Ministry; and the governments of France, Spain, Germany, Canada, Tunisia, Libya and Sudan.





"The SNC urgently requested that these parties support the Syrian people's and the Syrian Revolution's demands for international protection, the establishment of safe zones for civilians, and the establishment of humanitarian corridors for delivery of relief, medical, and other humanitarian needs. The SNC also demanded a prompt intervention to stop the massacres, which have reached the level of genocide and which coincide with the signing of the Arab League Protocol to send observers into Syria," the council said.





Mohamed Hamdo, a lieutenant colonel in the Free Syrian Army, underscored the ferocity of the assaults.





He said that government forces "used military jet fighters and bombed Jabal Al Zawya, including a mosque that contained around 100 civilians who were praying or using it as a refuge." Jabal Al Zawya is in the Idlib region in northwestern Syria.





Hamdo said the military also "destroyed the town of Idlib completely and bombed a hospital there. The problem is they are using women and children who are mounted on their tanks as they raid, making it impossible for us to hit back."





"We have information that they are preparing an attack to control the border crossing to Turkey. We are dispersing our FSA platoons to counterattack. They are using surface-to-air missiles, mortars, military jet fighters and artillery."





Activist groups also reported a surge in killings this week. The London-based Syrian Observatory for Human Rights reported a higher death toll of 111 on Tuesday and 121 on Monday. The Monday figure included 72 soldiers who tried to defect.





The civilian death toll so far Wednesday is at least 16, according to the Local Coordination Committees of Syria, an opposition umbrella group.





And, a video surfaced on social media websites of a boy's grisly killing in Homs during a missile attack Tuesday.





This violence comes as an Arab League advance team is headed to Damascus Thursday to prepare for the observer mission. There would be 100 observers in teams of 10
The United Nations estimates that about
250 people have died over a 48-hour period.
question: The United Nations estimates that about, answer: 250 people have died over a 48-hour period.