A UN envoy on Saturday urged foreign powers to work to avoid a collapse of vital Syrian institutions following the downfall of leader Bashar al-Assad, as diplomats gathered in Jordan for a conference on the crisis.

Geir Pedersen, the UN's special envoy for Syria, also backed a "credible and inclusive" political process to form the next government as he met US Secretary of State Antony Blinken.

"We need to make sure that state institutions do not collapse, and that we get in humanitarian assistance as quickly as possible," Pedersen said.

"If we can achieve that, perhaps there is a new opportunity for the Syrian people."

Top Arab, Turkish, EU and US diplomats are holding talks in the Jordanian Red Sea resort city of Aqaba less than a week after Islamist-led rebels toppled Assad.

Blinken, on a trip in which he met the leaders of Jordan, Turkey and Iraq, has repeatedly called for an "inclusive" process that reflects all the diverse ethnic and religious communities in Syria.

Meeting Pedersen, Blinken said the United Nations "plays a critical role" in humanitarian assistance and protecting minorities in Syria. (AFP)