Thousands of Syrians have fled their country in one of the biggest refugee exoduses of the 20 month war after rebels seized a border town.
The United Nations said 11,000 refugees had fled in 24 hours, most to Turkey.
Meanwhile, a senior UN official has warned an estimated four million people in Syria will need humanitarian aid by early next year.
John Ging, director of operations at the UN Office for the Coordination of Humanitarian Affairs, painted a bleak outlook for civilians caught up in the fighting.
"If the current rate of conflict continues at the current pace we can reasonably project that numbers in need to rise from 2.5m to 4m by the early new year," Mr Ging said.
"Every day our humanitarian colleagues on the ground are engaging with people who are ever more desperate, ever more fearful for their lives and for the lives of their families because of this conflict," he said.
The International Committee of the Red Cross said yesterday it could not keep up with the increasingly dire needs of civilians.
The Syrian Observatory for Human Rights, a UK-based group that compiles opposition activist reports, said at least 20 members of the Syrian security forces were killed when rebel fighters attacked a security headquarters in Ras al-Ain.
Thousands of residents poured out of the town, in the northeastern oil-producing province of Hasaka, 600km from Damascus.
Turkey's Prime Minister Tayyip Erdogan hit out at world powers on the UN Security Council over their inaction.
"It is very strange. There are currently atrocities being committed in Syria and these atrocities are being directed by a state leader," he said.
"How far will this go? When will the permanent members of the Security Council take responsibility?"
The Turkish state-run Anatolian news agency reported that 26 Syrian military officers had also arrived in Turkey with their families overnight in what it called the biggest mass desertion of senior soldiers from President Assad's forces in months.
The latest flight of refugees raised the total recorded by the United Nations to 408,000.