LAUSANNE -  Pessimistic envoys from the United States, Russia and Syria's neighbours met Saturday in Switzerland as Secretary of State John Kerry tried to revive hopes of a ceasefire for the war-torn country.

The talks marked Kerry's first encounter with his Russian opposite number Sergei Lavrov since a US and Russian-sponsored truce collapsed last month amid a ferocious Syrian offensive. But diplomats from all sides warned against hopes for a rapid breakthrough in Lausanne, and Moscow showed no sign of softening its strong support for Syrian President Bashar al-Assad.

Even as the diplomats gathered in a lakefront hotel, Moscow's flagship aircraft carrier set sail for the Mediterranean to support the Russian forces shoring up Assad's rule. Fierce fighting was continuing in the multi-front conflict, with Turkish-backed opposition fighters closing in on Dabiq, a symbolic stronghold of the Islamic State group.

And in Aleppo, Russian-backed government forces intensified their bombardment of the rebel-held east of the city, further damaging any prospect of a renewed ceasefire. Kerry and Lavrov, once joint sponsors of international peace effort, met ahead of the broader talks, but US officials insisted that their "bilateral track" remains dead.

Instead, with President Barack Obama adamant that US forces will not become caught up in the war, Kerry was hoping that talks with Russia and regional powers may yield new ideas.

"We are not pursuing this directly with the Russians bilaterally any more," a senior US official travelling with Kerry told reporters ahead of the meeting. "But just because the format has evolved doesn't mean that the underlying objectives have changed," he insisted.

Those objectives, he said, are a reduction in violence, more humanitarian access to besieged civilians and a political dialogue between the government and opposition. But both US and Russian officials played down hopes of a breakthrough on Saturday, and Kerry was due to fly on to London on Sunday to brief European allies on the new effort.

Lavrov told reporters on Friday he had no "special expectations" of progress. Iran also voiced scepticism, with a foreign affairs ministry spokesman saying: "I don't think we can have a lot of a hope for the outcome of this meeting." The talks come as Moscow faces down growing criticism over its backing for Assad's assault in divided Aleppo.

Air strikes hit rebel-held parts of Aleppo again Saturday, according to the Syrian Observatory for Human Rights, a British-based watchdog with a network of sources on the ground. Against this bloody backdrop, a leading opposition group slammed the talks, saying they would not stop the killing.

Abdal Ahad Stefo, deputy head of the Istanbul-based National Coalition, told AFP the negotiations "will only lead to wasting more time ... and the shedding of more Syrian blood".

Aleppo has been engulfed by some of the worst violence of the conflict since the collapse of last month's truce deal.

"I think we need to see what happens in the room to determine whether this is the beginning of a new process that continues in this format or not," said the senior US official.

On Friday, Lavrov had warned that Russia was not planning on presenting new initiatives on ways to resolve the conflict, which has claimed more than 300,000 lives since 2011.

Instead he called for "concrete steps" to implement earlier UN resolutions and specifically for opposition fighters to separate from "terrorist" militant groups.

Kerry and Lavrov were joined by UN Syria envoy Staffan de Mistura, as well as top diplomats from Turkey, Saudi Arabia and Qatar - all nations that back Syrian opposition forces.

Iran, a key Assad supporter, was being represented by Foreign Minister Mohammad Javad Zarif. Egypt, Iraq and Jordan were also set to be part of the meeting, the US official said.

The intensified bombardment has put increasing strain on rescue workers in besieged eastern Aleppo which is home to an estimated 250,000 residents.

More than 370 people, including nearly 70 children, have been killed in regime and Russian bombardment of eastern Aleppo since September 22, according to the Observatory.

Dozens of civilians, including children, have also died in rebel bombardment of regime-controlled western districts.

Buoyed by his forces' gains in Aleppo, Assad vowed to use victory there as a "springboard" to capture other rebel bastions, in remarks published Friday.


Meanwhile, President Barack Obama met on Friday with his national security team to discuss the fight against Islamic State and the war in Syria, the White House said.

Reuters had reported that in the meeting Obama and his advisers would consider military and other options in Syria as Syrian and Russian aircraft continue to pummel the city of Aleppo and other targets, US officials said.

US officials said they considered it unlikely that Obama would order US air strikes on Syrian government targets, and they stressed that he might not make any decisions at the National Security Council meeting.

A readout of the meeting released by the White House noted that the United States had broken off bilateral talks with Russia on reaching a ceasefire in Syria. It said Obama directed his team to continue multilateral talks with "key nations" to seek a diplomatic resolution to the civil war.

The brief summary made no mention of other US options in Syria.

US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov will return to Syria talks on Saturday, three weeks after the failure of their painstakingly drafted ceasefire.

Kerry has pointedly avoided new bilateral negotiations with Lavrov, and his invitation to the Turkish, Saudi, Qatari and Iranian foreign ministers to join them for talks in Lausanne, Switzerland, will broaden the discussion to include the most powerful backers of Syria's government and rebels.

Pressure is rising for a halt to a ferocious, three-week-old Syrian government offensive to capture the rebel-held eastern zone of Aleppo, where the United Nations says 275,000 civilians still live and 8,000 rebels are holding out against Syrian, Russian and Iranian-backed forces.