A top Syrian opposition figure says President Bashar Assad should have no role during a transitional period to end the country's civil war.

Former Prime Minister Riad Hijab said in Saudi Arabia on Friday that "confidence-building measures" should be in place ahead of the transitional period, such as release of detainees, lifting of a siege imposed on rebel-held areas and a halt to airstrikes.

Hijab is the coordinator of the opposition team that will negotiate with the Syrian government. He spoke shortly before some 20 foreign ministers gathered in New York to discuss civil war, the prospects of arranging a cease-fire and launching peace negotiations in 2016.

Last week, a two-day conference in the Saudi Arabian capital, Riyadh, sought to form a unified opposition front ahead of the talks.