A cease-fire brokered by the United States and Russia is set to begin at sunset in Syria amid mixed messages of commitment from various rebel factions but with verbal backing by President Bashar Assad's government.

Assad made a rare public appearance on Monday, attending prayers for the Muslim holiday of Eid al-Adha at a mosque in the suburb of Daraya, which surrendered last month after four years of government siege.

The cease-fire deal hammered out between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov in Geneva last week allows the Syrian government to continue to strike at the Islamic State group and al-Qaida-linked militants, until the U.S. and Russia take over the task in one week's time.

Rebel factions have expressed deep reservations about the deal.