A cease-fire was to go into force at 6 a.m. Thursday. The official Syrian Arab News Agency carried a statement from former U.N. Secretary-General Kofi Annan saying the country was experiencing "a rare moment of calm" after the deadline passed.
Turkish Foreign Minister Ahmet Davutoglu said Syrian forces must return to their barracks completely before a formal truce is considered in force.
"Reports of a partial withdrawal from some places have surfaced," he was quoted by Turkish news agency Today's Zaman as saying. "But pulling the forces out of the cities and maintaining the pressure on them should not be presented as a real withdrawal."
SANA reported that "an armed terrorist" group inside the country targeted a bus carrying military officers, killing 24 people roughly two hours after the deadline passed in Aleppo.
Davutoglu, during an interview with the BBC, said Syrian forces violated Turkish territory in fighting this week. Turkey, he said, would make "any preparations" to defend its borders, but stressed protecting Syrian civilians in their territory was the responsibility of the international community.
A U.S. State Department official told CNN on condition of anonymity that the White House was considering establishing a "buffer zone" along the Turkish border with Syria.