United Nations peace envoy Staffan de Mistura arrived in Damascus Friday to meet with Syria's foreign minister as part of efforts to end the country's nearly five-year war, an AFP photographer said.

De Mistura will meet Walid Muallem Saturday to discuss preparations for talks between government and opposition figures later this month, a UN source in Damascus told AFP.

The talks are the first step in an ambitious 18-month plan, endorsed by the UN, to bring about a political transition in Syria.

Before his visit, de Mistura met with opposition figures in Riyadh in a bid to confirm the talks' starting date as well as the composition of the opposition's delegation, an Arab source there said.

He also met ambassadors of countries that were involved in discussions on Syria in Vienna in October and November, in which both Tehran and Riyadh took part, the source told AFP.

De Mistura is also set to visit Iran in the coming days for talks aimed at defusing tensions between it and Saudi Arabia, which each back opposite sides in Syria's war.

De Mistura "believes that the crisis in Saudi-Iranian relations is a very worrisome development and stresses the need to ensure it does not cause a chain of adverse consequences in the region," said UN spokesman Stephane Dujarric.

The envoy would "assess the implication" of the crisis on the Syria peace effort, Dujarric added.

Syria's conflict erupted in 2011 with anti-government protests but quickly spiralled into a bloody multi-sided conflict that has left more than 260,000 people dead.