Syrian tanks and armoured vehicles swept into the coastal city of Latakia on Saturday and gunfire was heard in a district where thousands had protested against President Bashar Al-Assad, an activist group said.

The deployment took place a day after security forces shot dead 20 people during nationwide marches in which demonstrators called for Assad's overthrow and vowed to "kneel only to God".

Assad's military crackdown on the five-month protests, in which activists say over 1,700 civilians have been killed, has prompted new US sanctions on Damascus and criticism from Arab states after months of regional silence.

The British-based Syrian Observatory for Human Rights said around 20 military vehicles deployed on Saturday near the Ramle district of the Mediterranean city of Latakia, where 10,000 people had demonstrated on Friday.

"Heavy gunfire could be heard from 10.30 am until midday (0730 to 0900 GMT)," the group's head Rami Abdel Rahman said, adding that large numbers of people were fleeing the area.

He also reported that soldiers backed by loyalist gunmen, known as shabbiha, raided villages close to the northern town of Qusair near the Lebanon border, carrying out arrests.

Eleven people were killed by security forces in Qusair on Thursday, activists said, part of Assad's escalated military repression during the Muslim holy month of Ramadan which began two weeks ago.

Syrian authorities have barred most independent media, making it difficult to verify events on the ground in the unrest, one of a series of popular revolts against autocratic Arab leaders this year.

Authorities say 500 soldiers and police have been killed by armed groups who they blame for the violence. The state news agency SANA said three members of the security forces were killed on Friday.

Ramadan offensive

Since the start of Ramadan in early August, Assad has stepped up the military campaign, launching army assaults on the central city of Hama and the city of Deir al-Zor in the eastern Sunni Muslim tribal heartland. Assad's family, which has ruled Syria for 41 years, is from the minority Alawite sect.

US Secretary of State Hillary Clinton said on Friday Syria would be better off without Assad and called on nations that buy oil or sell arms to Syria to cut those ties.

"We urge those countries still buying Syrian oil or gas, those countries still sending Assad weapons, those countries whose political and economic support give him comfort in his brutality, to get on the right side of history," she said.

Syria's oil industry, with which the Assad family has close links, generates most of the state's hard currency from crude output of 380,000 barrels per day.

While Syria exports crude oil, its refinery capacity is not sufficient to meet domestic demand for fuel. Trading sources said Swiss oil traders Vitol and Trafigura agreed to supply state firm Sytrol with 60,000 tonnes of gasoline this week.

The global campaign group Avaaz urged European nations on Friday to impose immediate restrictions on purchases of Syrian oil to "dry up" funding of Assad's forces. It said more than 150,000 Avaaz members had signed a petition to that effect.

On Wednesday Washington imposed sanctions on Syria's largest bank and its biggest mobile telephone company, controlled by Assad's cousin Rami Makhlouf. The next day, US Ambassador to Damascus Robert Ford said more sanctions would follow if the Syrian authorities did not halt the violence. – Reuters