More than 4,000 Syrians have fled to Turkey to escape a crackdown on protests against President Bashar al-Assad and thousands more are sheltering near the border, officials and activists said on Saturday.
Fearing revenge from security forces for clashes in which authorities said 120 troops were killed this week, the refugees streamed out of the northern town of Jisr al-Shughour ahead of a military operation launched by the army there on Friday.
A senior Turkish diplomat said 4,300 Syrians had crossed the border and that Turkey was prepared for a further influx, though he declined to predict how many might come.
"Turkey welcomed a great many number of guests in the past in their times of most dire need. We can do that again," Foreign Ministry Deputy Undersecretary Halit Cevik was quoted as saying by state-run Anatolian news agency.
Refugees could be seen walking around the grounds of a camp at Boynuyogun where tents have been pitched inside an old hangar, and another camp at Yayladagi has been established in the grounds of a disused tobacco company.
At a third site, set up in fields close to the border but so far still empty, workers carried beds into tents on Saturday.
Radikal newspaper said Turkey would establish a buffer zone if migrant inflows from Syria exceed 10,000. Just inside Syria, thousands more people were gathering close to the frontier, according to an activist helping coordinate the movement of refugees.
"The border area has turned practically into a buffer zone," said the man, who identified himself only as Abu Fadi. "Families have taken shelter under the trees and there are 7,000 to 10,000 people here now."
Human rights groups say security forces have killed more than 1,100 Syrian civilians in increasingly bloody efforts to suppress demonstrations calling for Mr. Assad's removal, more political freedoms and end to corruption and poverty.
Thirty-six protesters were shot dead across Syria on Friday, activists said. Syrian authorities deployed helicopter gunships in the town of Maarat al-Numaan, they added, in the first known use of air power against unrest.
The government, which has blamed violence in the protest wave on "terrorists", said on Saturday the army had arrested two armed groups in Jisr al-Shughour after launching operations there in response to requests from residents. The state news agency SANA said they seized guns, explosives and detonators.
SANA also said that a group of journalists and photographers came under fire on Saturday from "terrorist groups" at the entrance to the town, but that none were wounded.
Some activists and residents said the fighting earlier in the week in Jisr al-Shughour was between members of the security forces after some mutinied over orders to shoot at protesters, and that many of the dead were civilians caught in the clashes.
Damascus has banned most foreign correspondents from the country, making it difficult to verify accounts of events.
The northwest border area, like other protest hotspots, is prone to tension between Syria's majority Sunni Muslims and Assad's Alawite sect, which dominates the Syrian power elite. The recent clashes hint at splits within the security forces, whose commanders are mainly Alawite and conscripts Sunni.
The protests were inspired by uprisings against other entrenched autocrats in the Arab world but do not appear to have become large or widespread enough to threaten Mr. Assad with the same fate as the toppled leaders of Egypt and Tunisia.
Britain, France, Germany and Portugal have asked the UN Security Council to condemn Assad, though veto-wielding Russia has said it would oppose such a move.
Denouncing Syrian government actions, the White House said Friday's "appalling violence" had led the United States to back the European draft resolution at the United Nations.
"The Syrian government is leading Syria on a dangerous path," the White House said.
A statement from the United Nations said Secretary General Ban Ki-moon was deeply concerned by the violence in Syria.
"The Syrian authorities have an obligation to protect their people and respect their rights. The use of military force against civilians is unacceptable," it said.
A UN spokesman said Mr. Ban had been trying to call Mr. Assad all week but was told that the president was "not available".
Foreign Minister Walid al-Moualem wrote to the Security Council accusing the opposition of violence and sabotage, al Arabiya television said. Foreign governments were basing their views on "inaccurate information", it said.
Mr. Moualem's letter asked for UN help to combat "extremism and terrorism". Damascus wanted dialogue with the opposition, he said, reiterating an official position that opposition leaders say is not credible given the military crackdown.
Syrian authorities have repeatedly portrayed anti-government protesters as armed and violent.
State television said on Friday well-armed "terrorist groups" had burned police buildings and killed members of the security forces in Maarat al-Numaan, which lies 55 kilometres south of Syria's second city Aleppo on the highway to Damascus.
A demonstrator, speaking by telephone from Maarat al-Numaan, said the protests there had been peaceful. "The security forces let us protest, but when they saw the size of the demonstration grow, they opened fire to disperse us.
"During the protest, two officers and three soldiers refused to open fire so we carried them on our shoulders. After that, we were surprised to see helicopters firing on us."
A 40-year-old from Jisr al-Shughour, with a bullet still in his thigh, also described mutiny in Syrian ranks.
"Some of the security forces defected and there were some in the army who refused the orders of their superiors," he said. "They were firing on each other."