Top US diplomat John Kerry flew into Russia Thursday to press President Vladimir Putin over Syria peace efforts and targeting militant groups, as leader Bashar al-Assad said he has never faced pressure from Moscow to go.
The US Secretary of State was set to meet Putin in the Kremlin with Washington reportedly ready to offer to cooperate with Moscow in joint military action against the Islamic State (IS) group and the Syrian branch of Al-Qaeda, Al-Nusra Front.
Kerry did not deny the proposal -- reported by the Washington Post Thursday -- and it would mark a dramatic shift if it brought together Assad's key backer Moscow and his major foe Washington.
The US envoy will also look to try to revive a shattered ceasefire and push Putin on a stalled peace process as little progress has been made towards a hoped-for resumption of Syria talks.
Ahead of the meeting in Moscow, there appeared little indication that Assad was set to budge on the major issue hampering peace talks -- his own future.
Speaking to NBC News in Damascus, Assad insisted Putin and Russian Foreign Minister Sergei Lavrov had never raised the issue of his departure or a political transition.
"Only the Syrian people define who's going to be the president, when to come, and when to go. They never said a single word regarding this," he said.
Moscow and Washington have backed a roadmap that calls for a nationwide ceasefire and Geneva-based talks on a "political transition".
A landmark partial ceasefire they brokered in February has since all but collapsed amid continued heavy fighting.
UN Syria envoy Staffan de Mistura on Thursday urged Moscow and Washington to push for a resumption of the talks next month.
The talks "have a target date of August," de Mistura said, adding that they need to be "a credible beginning of a roadmap towards a political transition."
Currently, Russian forces in Syria are operating in support of Assad's regime against a variety of rebel factions while a US-led coalition focuses its fire on the Islamic State group.
The Washington Post, citing sections of what it said was a draft proposal from the United States, reported that US and Russian commanders would set up a joint command and control centre in Jordan to direct intensified air strikes against the militant groups.
Any deal between the great power rivals would be controversial, since for many -- including critics of US President Barack Obama in Washington -- it would amount to a tacit acceptance of Putin's efforts to shore up Assad's regime.
Ahead of flying to Moscow, Kerry did not deny the report but refused to discuss the proposal in detail until he had been to see Putin.
Kremlin spokesman Dmitry Peskov also declined to comment on the report before Moscow had seen what Washington had to offer.
Syria's conflict began in 2011 with the repression of anti-government demonstrations and has evolved into a multi-front war that has left more than 280,000 dead and forced millions from their homes.
Efforts to bring an end to the war have taken on greater urgency since the emergence of the Islamic State group, which seized control of large parts of Syria and neighbouring Iraq in mid-2014.
The militants have committed widespread atrocities and organised or inspired a wave of attacks across the Middle East and in Western cities.
Operations by both the US coalition and Russia have seen the group lose territory recently and Moscow said on Thursday said it had carried out more than 50 strikes against IS near the Syrian city of Palmyra over the past three days.
On Thursday alone, six Tupolev bombers flew out of an airbase in Russia and conducted strikes east of Palmyra, near the cities of Arak and Sukhna, as well as in the Homs region, it said.
IS group fighters were forced out of Palmyra by Syrian regime forces in March with Russian backing, but Arak and Sukhna remain out of the government's control.
Despite repeated announcements of ceasefires, Syrian government forces have continued offensives on a range of fronts, with fighting especially heavy around second city Aleppo in recent weeks.
Fresh air strikes on two rebel-held neighbourhoods of Aleppo killed at least 12 civilians on Thursday, the Syrian Observatory for Human Rights said.