Regime forces halted heavy shelling and other major attacks in line with the truce that began at dawn Thursday, though there were accusations of scattered violence by both sides. The government ignored demands to pull troops back to barracks, however, defying a key aspect of the plan, which aims to calm a year-old uprising that has killed 9,000 people and has pushed the country toward civil war.
"The onus is on the government of Syria to prove that their words will be matched by their deeds at this time," U.N. Secretary-General Ban Ki-moon told reporters in Geneva. He said the world was watching with skeptical eyes.
"This cease-fire process is very fragile. It may be broken any time," Ban added, saying "another gunshot" could doom the truce.
The presence of tanks and troops could discourage any large gatherings, but the leader of the opposition Syrian National Council, Burhan Ghalioun, urged Syrians to demonstrate peacefully on Friday. "Tomorrow, like every Friday, the Syrian people are called to demonstrate even more and put the regime in front of its responsibilities - put the international community in front of its responsibilities."
A massive protest would be an important test of the cease-fire - whether President Bashar Assad will allow his forces to hold their fire and risk ushering in a weekslong sit-in or losing control over territory that government forces recently recovered from rebels.
So far, the military crackdown has prevented protesters from recreating the powerful displays of dissent seen in Egypt's Tahrir Square, where hundreds of thousands of people camped out in an extraordinary scene that drove longtime leader Hosni Mubarak from power.
If the truce holds, it would be the first time the regime has observed an internationally brokered cease-fire since Assad's regime launched a brutal crackdown 13 months ago on mass protests calling for his ouster.