Head of the Syrian National Council, Burhan Ghalioun, urged Syrians to demonstrate on the day of the ceasefire. He also urged the international community to provide protection to Syrians who take to the streets by sending observers.

"We call on the people to demonstrate and express themselves... The right to demonstrate is a principle point of the plan" of UN-Arab peace envoy Kofi Annan, Ghalioun who leads the exile umbrella opposition organisation told AFP in Beirut.

The ceasefire appeared to be holding nearly more than five hours after it took effect at 6:00am on Thursday, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

The truce deadline was part of a six-point peace plan that Syria agreed with Annan, under which Assad's government is to respect freedom of association and the right to demonstrate peacefully.

"There is no value for the Annan plan if it does not transfer the country into having a pluralist and democratic government, and the first step in this transitional process is to uphold the people's right to demonstrate, freedom of expression and press," said Ghalioun.

"We call upon the countries that back the Annan plan to monitor its implementation in full, mainly the right to demonstrate... and to provide the means to protect the people if the regime violates the plan.

"International observers should be on the ground as soon as possible," he added.

Just hours before the ceasefire deadline, Assad's forces unleashed a lethal offensive against protest centres, killing 25 civilians on Wednesday, including 10 in the rebel stronghold of Rastan, said the Observatory.

Syria has been cracking down on Arab Spring-inspired dissent since mid-March 2011 in violence the Observatory says has killed more than 10,000 people. The United Nations has put the toll at more than 9,000 dead.