Activists who oppose the regime of President Bashar Assad said some Syrian troops have clashed with rebels near the border with Turkey.
However, there was no sign of the widespread shelling and rocket attacks that had been a daily occurrence prior to Thursday's cease-fire.
The U.N. calls the current situation fragile. The truce, the first brokered by the international community since the Syria crisis erupted, calls for the Syrian government to allow peaceful protests.
A major outbreak of violence at a chaotic rally could give government forces a pretext for ending the peace plan, which aims to calm the uprising that has killed 9,000 people and pushed the country toward civil war.
The Associated Press contributed to this report.