By Lisa Barrington and Roberta Rampton

BEIRUT/HANGZHOU, China (Reuters) – The United States and Russia will work in the next few days on a deal to curb fighting in Syria and build cooperation in the fight against terrorism, their leaders said on Monday, as blasts claimed by Islamic State killed dozens across the Arab nation.

The former Cold War enemies have been trying to broker a new truce after a ceasefire agreed in February unravelled in weeks, with Washington accusing Syrian President Bashar al-Assad’s forces – which are backed by Russia – of violating the pact.

U.S. President Barack Obama described talks with Russian counterpart Vladimir Putin as tough but productive after their meeting at the G20 summit in China. Putin said the two men had understood each other and an agreement on ways to significantly reduce the violence in Syria could be reached in days.

“We have had some productive conversations about what a real cessation of hostilities would look like, that would allow us both, the United States and Russia, to focus our attention on common enemies, like ISIL and Nusra,” Obama said, referring to Islamic State and the hardline Nusra Front.

“We haven’t yet closed the gaps in a way where we think it would actually work,” he said, but added that U.S. Secretary of State John Kerry and Russian foreign minister Sergei Lavrov would “keep working at it over the next several days”.

Putin told journalists there was a convergence of views between Russia and the United States. He said it was premature to give details about the terms of an agreement, but that the two nations would strengthen cooperation on fighting terrorism.

Truce talks were complicated on Sunday as government forces and their allies laid siege to the rebel-held eastern side of Aleppo, Syria’s largest city before the war which Assad is determined to fully recapture. His gains have relied heavily on Russian air support since September last year.

Adding to the carnage, six blasts on Monday hit west of Damascus and the government-held cities of Homs and Tartous, as well as the Kurdish-controlled northeastern province of Hasaka, state media and a monitoring group said.

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

CONFLICTING AGENDAS

More than five years of civil war have cut Syria into a patchwork of territories held by the government and an often competing array of armed factions, including Kurdish militia fighters, a loose coalition of rebels groups, and Islamic State.

Obama and Putin discussed getting humanitarian aid into the country, reducing violence, and cooperating on combating militant groups, the U.S. administration official said.

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

But in talks earlier on Monday, Kerry and Lavrov were unable to come to terms on a truce for the second time in two weeks, with U.S. officials stressing they would walk away if a pact could not be reached soon.

Russia says it cannot agree to a deal unless opposition fighters, backed by the United States and Middle East allies, are separated from al Qaeda-linked militants they overlap with in some areas. For Washington, the priority is stabilising Syria so as to destroy Islamic State.

NATO Turkey ally on Sunday said rebels it was backing had gained control of all areas on its border that had been held by the jihadists, depriving the ultra-hardline Islamist group of its main route to the outside world.

The announcement came some 10 days after Turkey launched its first major military incursion into Syria since the start of the war in 2011, an operation aimed as much at preventing further Kurdish territorial gains as at driving back Islamic State.

“Syrian citizens in our country and those would want to migrate from Syria can now live more peacefully in their own land,” Erdogan said, adding the Turkish incursion posed no threat to Syria’s territorial integrity.

He renewed calls for an internationally-policed “no-fly zone” to protect displaced civilians and help stem refugee flows. But the idea, which he also raised at a G20 summit in Turkey a year ago, has failed to gain traction with Western allies who fear it would mean a deeper military commitment.

DOZENS KILLED

Two of the explosions on Monday hit the Arzouna bridge area at the entrance to the Mediterranean city of Tartous, the Syrian Observatory for Human Rights and state news agency SANA said. The Observatory and a city hospital put the death toll at 35.

Syrian state television said the first explosion was a car bomb and the second a suicide belt detonated as rescue workers arrived. The blasts hit during a summer festival at Tartous, whose beaches recently featured in a government tourism video.

A car bomb meanwhile struck the city of Homs, around 80 km (50 miles) east of Tartous. The Observatory said the explosion hit an army checkpoint and four officers were killed.

West of Damascus, there was an explosion near the town of al Saboura, killing one person and injuring three, according to a police commander quoted by state media.

A motorbike also exploded in the centre of the northeastern city of Hasaka, which is controlled by the Kurdish YPG militia. The Observatory said the blast killed three members of a YPG-affiliated security force and that a percussion bomb also went off in the province’s Qamishli city.

The Kurdish YPG militia, a critical part of the U.S.-backed campaign against Islamic State, took almost complete control of Hasaka city in late August after a week of fighting with the government.

The YPG controls swathes of northern Syria where Kurdish groups have established de facto autonomy since the start of the Syrian war, much to the alarm of neighbouring Turkey, which fears the creation of a Kurdish enclave in northern Syria would fuel Kurdish separatist ambitions at home.

Ankara has demanded that Kurdish militia fighters remain east of the Euphrates river, something Washington has promised they will do. Brett McGurk, the U.S. envoy to the anti-Islamic State coalition, visited Syria last week and emphasised “the need for strict adherence to prior commitments, a State Department spokeswoman said.

(Additional reporting by Kinda Makieh in Damascus and Ahmed Tolba in Cairo, Lesley Wroughton and Arshad Mohammed in Washington, Vladimir Soldatkin in Hangzhou, Humeyra Pamuk and Edmund Blair in Istanbul; Writing by Nick Tattersall; Editing by Giles Elgood and Anna Willard)