The United States and Russia came up short Sunday on an agreement to end more than five years of civil war between Syria’s Russian-backed government and US-supported rebels.

The negotiations were to continue Monday, even as President Barack Obama voiced scepticism the diplomacy would pay off.

Russia and the US have been striving for weeks to secure a ceasefire between Syrian President Bashar Assad’s government and moderate rebels that would expand access for hundreds of thousands of civilians caught in the crossfire.

The strategy has hinged on an unlikely US-Russian military partnership against extremist groups operating in Syria.

But beyond the Islamic State and al-Qaeda, the two powers have conflicting views about who fits in that category.

“We’re not there yet,” Obama said on the sidelines of an economic summit in Hangzhou China, where across town US Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov were trying to hash out the deal.

“It’s premature for us to say that there is a clear path forward, but there is the possibility at least for us to make some progress on that front.”

A senior State Department official said the talks hit a stumble on Saturday when Russia pulled back from agreement on issues the US negotiators believed had been settled.

The conflict has killed as many as a half-million people since 2011 and caused millions of Syrians to flee from their homes, contributing to a global migration crisis.

Truce talks complicated by fresh violence

A fighter from the Jaish al-Islam (Islam Army) in the rebel-held stronghold of Douma. Photo: Getty

Amid the chaos, IS has emerged as a global terror threat.

Syria’s festering conflict has left 290,000 dead, including two explosions which killed 34 people at the entrance to Tartous on Monday.

Islamic State fighters carried out the suicide attacks, its Amaq news agency said.

Turkish President Tayyip Erdogan said he was working with the US-led coalition and Russia to try to establish a ceasefire in Aleppo before the Eid al-Adha religious holiday expected to start around September 11.