Tillerson meets Syria opposition in Amman

US Secretary of State Rex Tillerson met Syrian opposition negotiators in Jordan on Wednesday for closed-door talks in the wake of a January peace summit hosted by regime backer Russia.

The opposition and Kurdish groups had boycotted the congress, held just days after a ninth round of United Nations-led talks in Vienna failed to yield progress towards ending Syria's devastating conflict.

The West views Russia's Syria peace efforts with suspicion, concerned that Moscow is seeking to sideline the UN process.

But the US acting assistant secretary of state, David Satterfield, said on Wednesday that the fallout had been limited.

"We got in the end a communique which validated the UN role," Satterfield said before Tillerson's meeting in Amman. "So this game, this theatre that was Sochi... finally came out in a way that did no damage."

Despite Moscow insisting Syrian society would be fully represented at Sochi, almost all of the 1,400 delegates were pro-regime.

They agreed to set up a commission to re-write the country's post-war constitution. 

About 150 Syrian civil society groups accused the UN of rewarding Russia by dispatching its special envoy Staffan de Mistura to the congress.

The Syrian conflict began when the Baath regime, in power since 1963 and led by Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.

The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.