Turkish Prime Minister Recep Tayyip Erdogan, right, flanked by the Syrian opposition coalition leader Mouaz al-Khatib, waves to people as he addresses residents of a Turkish village near the Syrian border in Sanliurfa, Turkey on Sunday.
ANTAKYA, Turkey — Opposition groups in Syria said Sunday that President Bashar Assad’s forces had killed at least 150 civilians at a petrochemical university in the central part of the country, one of the worst massacres of the 21-month uprising.
Meanwhile, the international envoy seeking to end Syria’s civil war warned that the failure of the government and the rebels to pursue a political solution could lead to the “full collapse of the Syrian state” and threaten the world’s security.
Lakhdar Brahimi, who represents the United Nations and the Arab League, said that as many as 100,000 people could be killed in the next year as Syria moves toward “Somalization” and rule by warlords.
Opposition groups that monitor the death toll said as many as 400 people — more than double the typical daily death toll — were killed Saturday.
About half of them were civilians slain in an alleged mass killing carried out by government troops at a petrochemical university in central Syria, opposition groups reported.
The government announced Saturday that it was in control of Deir Baalba, a suburb of the central city of Homs, after having surrounded the rebel-held town about a month ago.
Opposition groups, whose reports could not be independently verified, said government forces committed a massacre in the battle for the town.
Walid Faris, a spokesman for the Revolutionary Council of Homs, said by phone that Deir Baalba is surrounded by villages populated by members of the Alawite sect of Assad.
During the army counteroffensive, it was hit heavily by artillery shells and mortar rounds, he said, and the rebel Free Syrian Army managed to clear a small evacuation route to get most civilians out of the conflict zone. But some remained.
The count was based on reports from government soldiers sympathetic to the rebels and from residents of a nearby village, Mr. Faris said.
Mr. Brahimi has reported little progress in his mission to push forward a peace plan for Syria first presented in June at an international conference in Geneva.
The Syrian government has remained mum on Mr. Brahimi’s plan, which he has pushed in the past week in meetings with Assad in Damascus, with top Russian officials in Moscow, and on Sunday with the head of the Arab League in Cairo.