Kerry says US-Russia talks on Syria 'making progress'

US Secretary of State John Kerry said Tuesday talks with Russia about cooperation in Syria were "making progress", adding he hopes next month to announce new steps aimed at ending the fighting.

Russia and the United States support opposing sides in Syria's five-year war, which has left 280,000 people dead and forced half the population to flee their homes.

Moscow and Washington co-chair a 22-member contact group working to end the war but a truce brokered by the pair in February has faltered amid heavy fighting.

A man looks on as Syrian civil defence workers look for survivors under the rubble of a collapsed building following air strikes in Aleppo on July 17, 2016 ©Thaer Mohammed (AFP/File)

Kerry held marathon talks with Russian President Vladimir Putin and his Foreign Minister Sergei Lavrov in Moscow last week. They agreed "concrete steps" to revive the ceasefire and tackle jihadist groups in Syria, although details have not been made public.

Speaking after fresh talks on Tuesday with Lavrov on the sidelines of a regional meeting in Laos, Kerry said discussions were edging forward.

"I think we are making progress," he told reporters.

"If we do our work as effectively as it's been done over the last days since I was in Moscow my hope would be that somewhere in early August... we would be in a position to be able to stand up in front of you and tell you what we're able to do," he said.

"In simple terms... what we're trying to do is strengthen the cessation of hostilities, provide a framework which allows us to actually get to the table and have a real negotiation."

On Monday US Defense Secretary Ashton Carter struck a different note, saying Russia and America remained far from finding common ground on how to end the war.

Repeated rounds of international negotiations to end the conflict, which erupted in 2011 after Assad's regime unleashed a brutal crackdown on a pro-democracy revolt, have run aground.