An uneasy ceasefire between the Syrian army and government forces took hold Thursday, following a night of violence in the western city of Homs.

But despite the halt in fighting, which according to sources came an hour after the 6am deadline, President Bashar al-Assad's forces continued to defy the terms of the United Nations-brokered peace plan by not returning to their barracks.

And Assad, who has broken promises to halt bloodshed in the past, dealt the fragile peace a further blow on Wednesday when he declared that his forces reserved the right to respond to any aggression.

The focus now turns to Friday, when activists have called for the largest demonstrations against the continued rule of President Bashar al-Assad in a move set to test the regime's willingness to hold to the truce.

The Syrian people will go out tomorrow and it will be the biggest possible (demonstration) so that the Syrian people can express their will, Burhan Ghalioun, the chairman of the opposition Transitional National Council, told Reuters by telephone.

We will see tomorrow if (the government) will keep its commitment. While we call on the Syrian people to protest strongly... we ask them to be cautious because the regime will not respect the ceasefire and will shoot, Ghalioun said.

It was a bloody night - there was heavy shelling on the city of Homs, but now it is calm and there is no shooting, Reuters quoted an activist saying.

There are no signs of a pullback - the tanks, snipers and armed forces are still visible across the city, he added.

The chairman of the London-based Syrian Human Rights Observatory, Rami Abdel Rahman, said: An hour after the ultimatum expired, the situation is calm in all regions.

The UN estimates over 9,000 have died since the Assad regime started clamping down on opposition demonstrations 13 months ago.