Hangzhou, China: The United States indicated Sunday it was close to a deal with Russia on stemming the violence in Syria’s brutal civil war, with President Barack Obama saying they were ‘working around the clock’.

Moscow and Washington support opposite sides in the Syrian conflict, which erupted in March 2011 after President Bashar al-Assad unleashed a brutal crackdown against a pro-democracy revolt.

Successive rounds of international negotiations have failed to end a five-year conflict that has left more than 290,000 people dead and forced millions to flee, a key contributor to migrant flows into Europe.

‘It is a very complicated piece of business,’ Obama told reporters.

‘You have the Assad regime which has been killing its own citizens with impunity, supported by the Russians and the Iranians’ he said, while the the moderate opposition was ‘often outgunned’.

Russia is one of Assad’s most important international backers while the US supports Syria’s main opposition alliance and some rebels, with other countries and forces also involved.

‘Trying to corral all of those different forces into a coherent structure for negotiations is difficult,’ Obama said after meeting British premier Theresa May ahead of the G20 summit.

‘But our conversations with the Russians are key.’

A senior State Department official said a deal was close, and could be announced by Secretary of State John Kerry and his Russian counterpart as soon as Sunday, but some issues remained to be resolved.

‘John Kerry and his counterpart, Sergei Lavrov, have been working around the clock, as well as a number of other negotiators to see what would a real cessation of hostilities would look like,’ Obama said.

‘We’re not there yet.’

Fears for Aleppo

If Lavrov and Kerry are to meet in Hangzhou on Sunday their talks would be devoted to Syria, the Russian minister’s spokeswoman told AFP.

The US and Russia co-chair a UN-backed humanitarian taskforce for Syria, which has been struggling to ensure access for desperately needed aid across the country.

The battered second city Aleppo, which is divided between government and opposition control but surrounded by loyalist forces, has emerged as a major concern with urgent calls for a ceasefire to alleviate a humanitarian catastrophe.

The talks in Hangzhou are the latest round of diplomacy on Syria, after marathon negotiations between Kerry and Lavrov in Geneva last week failed to yield a final deal.

Kerry then listed two main priorities to ensure any new ceasefire holds: responding to violations by the Damascus regime and checking the rising influence of the former al-Nusra Front.

That group has renamed itself Fateh al-Sham Front after renouncing its status as al-Qaeda’s Syrian affiliate, but Kerry stressed that ‘Nusra is al-Qaeda, and no name change by Nusra hides what Nusra really is and what it tries to do’.

Earlier truces have rapidly deteriorated, and Obama warned Sunday that the US was approaching the talks ‘with some scepticism’.

‘But it is worth trying,’ he said.

‘To the extent that there are children and women and innocent civilians who can get food and medical supplies and get some relief from the constant terror of bombings, that’s worth the effort.’