At least 23 people have been killed by security forces in Syria, many of them when the army attacked a northernwestern town, activists say.
A Syrian opposition figure told the AP news agency by telephone that tanks shelled Maarat al-Numan on Friday, after thousands of protesters overwhelmed security officers and torched the courthouse and police station.
Syria's state-run television appeared to confirm at least part of the report, saying gunmen had opened fire on security headquarters in the town, in Idlib province, causing casualties among security officials.
Witnesses said helicopter gunships fired machineguns to disperse a large pro-democracy protest in the town, in the first reported use of air power to quell protests in Syria's uprising.
The Syrian Observatory for Human Rights said no killings were
reported in the assault by the helicopters.
"At least five helicopters flew over Maarat al-Numaan and began firing their machineguns to disperse the tens of thousands who marched in the protest," a witnesses giving his name as Nawaf told Reuters by telephone.
"People hid in fields, under bridges and in their houses, but the firing continued on the mostly empty streets for hours".
Maarat al-Numan is located near the Turkish border, 40km from Jisr al-Shughur, where state television earlier said the army had begun operations.
Anti-government protests were held in many cities across the country after Friday prayers.
An activist in Damascus told Al Jazeera he counted at least 14 separate rallies in and around the capital, the largest number since the uprising began in March.
Security forces shot dead two protesters when they fired at a rally in the Qaboun district of Damascus, the London-based Syrian Observatory for Human Rights said.
In-depth coverage of escalating violence across Syria
The group said nine protesters were also killed in the Mediterranean port city of Latakia.
A resident in Deraa in the south of the country told Al Jazeera that two protesters had been killed there.
Security forces also shot dead two civilians in a village in the southern Hauran Plain, residents said.
"There was a demonstration of 1,000 people when the 'Amen' [security police] fired from their cars," one of the residents of Busra al-Harir village said, giving the names of the dead protesters as Adnan al-Hariri and Abdelmuttaleb al-Hariri.
Syrian state television said a member of the security forces, whom the television described as "preservers of peace", was shot dead by gunmen in Busra al-Harir, but residents say no policemen were killed and that the demonstration was peaceful.
The government said military operations in Jisr al-Shughur were aimed at restoring security in the town, where authorities said 120 security personnel were killed by "armed groups'' last week.
Activists said the security forces were shot by government troops, after they refused to open fire on civilians.
State television said "that in response to people's calls, units from the Syrian Arabic army started its duties in Jisr al-Shughur ... to arrest armed members".
But a resident of Jisr al-Shughur who fled the town on Friday morning, making his way towards the Turkish border to seek refuge, denied the government's claims that there were armed gangs in the town.
"All the accusations of residents sheltering gangs are false," he told Al Jazeera. "And we never asked the army for help or to enter our city. It is them firing on us."
The resident said he had seen the army shooting at fleeing villagers with machine guns.
"They have burned down all the crops in surrounding fields and the villagers are fleeing to the nearby mountain," he said.
State television said armed gangs were burning the fields around the town.
UN condemns Assad
Britain, France, Germany and Portugal have asked the United Nations Security Council to condemn the Syrian president, though veto-wielding Russia has said it would oppose such a move.
Denouncing the Syrian government's 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.
Syrian state television said earlier that well-armed "terrorist groups" had burned police buildings and killed members of the security forces in Maarat al-Numaan, which lies 55km south of Syria's second largest city, Aleppo, on the highway to Damascus.
Syrian Foreign Minister Walid al-Moualem wrote the UN Security Council a letter, saying foreign governments were basing their views on "inaccurate information".
The letter asked the UN to help combat "extremism and terrorism" and said that Damascus wanted dialogue with the opposition.
A UN spokesperson said that Secretary-General Ban Ki-moon had been trying to call Assad all week but was told that the president was "not available."
Reports in the last days of an imminent military operation in the town have prompted an exodus of refugees to nearby Turkey.
But Reem Haddad, the information ministry spokeswoman, told Al Jazeera that people leaving the town were "fleeing from armed groups".
She said "a lot of citizens" had asked the army to intervene and that there was "a state of absolute terror" in the area.
More than 2,800 Syrians have fled into the neighbouring country to escape the unrest in Jisr al-Shughur and other towns, according to the UN and Turkish officials.
|Refugees in Altinozu held banners reading 'Protect Jisr al-Shughur from Assad' and 'Thanks to Erdogan' [Reuters]
Most refugees are being housed at a camp in Yayladagi, a town about 10km from the border and 25km from Jisr al-Shughur.
Dozens of white tents have been set up in the camp, and ambulances have been carrying wounded people to hospitals in Antakya, the capital of Turkey's southern Hatay province.
The Turkish government has largely barred journalists from interacting with the refugees. Police guard the entrance to the camp, and local officials have been instructed not to talk to the media.
Turkish officials say they are preparing for the possibility of more refugees in the coming days.
Recep Tayyip Erdogan, Turkey's prime minister, has condemned Syria's crackdown on protesters as "inhumane'' and pledged to keep his country open for Syrian refugees.
Lebanon, Syria's neighbour to the west, has already absorbed about 5,000 refugees, though the UN says it is a "fluid population" and some of the refugees have already returned home.
Human rights groups say the Syrian crackdown has killed more than 1,300 people, most of them unarmed civilians. The government says a total of 500 security forces have been killed.