A cessation of hostilities in Syria was largely holding on its first full day on September 13, with only minor violations reported.
The cease-fire deal, brokered by Russia and the United States, has been described by U.S. Secretary of State John Kerry as possibly the "last chance to save a united Syria."
In the northern city of Aleppo, the scene of heavy fighting in recent months, opposition activists said rebel-held parts of the city were calm.
Turkey's state-run news agency said 20 UN trucks have left the country to deliver humanitarian aid to Aleppo.
The British-based Syrian Observatory for Human Rights reported sporadic violence carried out by both government and rebel forces in Hama Province and Damascus.
The monitoring group said it had not recorded a single civilian death from fighting in the 15 hours since the cease-fire came into effect.
If the cease-fire holds for a week, the United States and Russia are to carry out coordinated air strikes against Jabhat Fateh al-Sham, formerly the Al-Qaeda-linked Al-Nusra Front, and Islamic State militants. The truce does not apply to these two extremist groups.