Syrian security forces Tuesday fired on a mass protest of thousands in the city of Homs demanding the fall of the regime, hours after the authorities vowed to suppress an 'armed revolt' in the country.

Three army officers and three children were killed by 'armed criminal gangs' around the city, Syrian authorities announced.

"The sit-in was dispersed with force. There was heavy gunfire," an activist reached by telephone told AFP, without being able to give details of possible casualties.

He said the security forces very early Tuesday swarmed into Al-Saa Square, where some 20,000 people were staging a mass sit-in, scattering protesters who had vowed not to leave until President Bashar al-Assad stepped down.

The action came just hours after the government late on Monday vowed to suppress 'armed revolt' it said was undermining security in the country.

"The latest incidents have shown that... armed Salafist groups, particularly in the cities of Homs and Banias, have openly called for armed revolt," said an interior ministry statement carried by the official SANA news agency.

It accused such groups of killing soldiers, policemen and civilians, and of attacking public and private property, and warned that "their terrorist activities will not be tolerated."

The authorities 'will act with determination to impose security and stability in the country' and will "pursue the terrorists wherever they are in order to bring them to justice and end the armed revolt", it said.

The demonstrators arrived in their thousands at Al-Saa Square on Monday, many setting up tents, a day after 11 people were killed by security forces in Homs and a nearby town during a day of massive nationwide protest.

Inspired by popular uprisings which toppled hardline rulers in Tunisia and Egypt, the protesters vowed not to leave Al-Saa Square in the centre of Homs until Assad's regime fell.

They dismissed as insufficient a weekend pledge by Assad that he would lift nearly five decades of draconian emergency law and demanded the release of all political prisoners and an end to arbitrary arrests.

"More than 20,000 people are taking part in the sit-in at Al-Saa Square (Clock Square) and we have renamed it Tahrir Square like the one in Cairo," rights activist Najati Tayyara had earlier told AFP from Homs.

The sit-in protest was a copy of demonstrations in Egypt which forced out veteran president Hosni Mubarak in February after 18 days of protests in Cairo's emblematic Tahrir Square.

The embattled Assad, facing unprecedented popular protests since March 15, pledged on Saturday to lift the emergency law imposed by the ruling Baath Party when it seized power in 1963.

His promise to end martial law and bring in a new government tasked with implementing reform was deemed insufficient by activists who also want an end to the iron-fisted rule of the Baath party.

In the Homs region, three soldiers and three children died at the hands of criminals, the authorities said.

"Armed criminal gangs who block roads and spread fear in the area, came upon General Abdo Khodr Al-Tellawi, his two children and his nephew, and killed them in cold blood," the official news agency SANA reported. The victims' bodies were "mutilated", SANA added.

Two other officers "fell as martyrs to armed criminal gangs' bullets in Homs", the agency said.

Since the beginning of the protest movement more than a month ago, the authorities have repeatedly blamed violence on 'armed gangs'.

Foreign Minister Walid Muallem said Syria will proceed with reforms as promised, but warned against 'sabotage' by protesters, SANA reported.

At least 200 people have been killed by security forces or plain-clothes police since the start of the protest movement, according to Amnesty International.