BEIRUT – Syria’s opposition called for widespread protests today to test the regime’s commitment to an internationally brokered cease-fire that the U.N. chief described as so fragile it could collapse with a single gunshot.

Regime forces halted heavy shelling and other major attacks in line with the truce that began at dawn Thursday. 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.