Paris: The United States is to offer to cooperate with Russia in joint military action against the Al-Nusra Front and Islamic State extremist groups in Syria, a media report said on Thursday.
US Secretary of State John Kerry, who was on his way to Moscow for talks with President Vladimir Putin, did not deny the Washington Post report, but refused to discuss the proposal in detail until he had been to the Kremlin.
According to the Post, which cited sections of what it said was a draft agreement, US and Russian commanders would set up a joint command and control centre to direct intensified air strikes against the groups.
Currently, Russian forces in Syria are operating in support of Bashar al-Assad's regime against a variety of rebel factions while a US-led coalition focuses its fire on the Islamic State jihadist group.
Any deal between the great power rivals would be controversial, since for many - including critics of President Barack Obama in Washington - it would amount to a tacit acceptance of Putin's efforts to shore up Assad's regime.
Kerry was due in Moscow later today and was to hold talks first with Putin at the Kremlin then tomorrow with his opposite number Foreign Minister Sergei Lavrov.
Asked if he wanted to comment on the reported US offer of a military pact, Kerry said: "I don't right now. I'll have comments. I'm going to Moscow, meeting with President Putin tonight, and we'll have plenty of time to talk about it."
"I'll give you all a sense of where we are," he added.
According to the Post, Kerry was to propose to Putin that Russia and the United States set up a "Joint Implementation Group" or JIG to "enable extended coordination" between their militaries on the Syrian battlefields.
Both the Islamic State and the Al-Nusra Front are defined as terrorist groups by the UN Security Council, and they are not party to the much-breached ceasefire in place between Assad's forces and more moderate rebel groups.
But, while the Islamic State's so-called "caliphate" has global ambitions, Al-Nusra - an affiliate of Al-Qaeda - has concentrated on battling Assad, fighting alongside other rebel groups backed by US allies.
Any deal between Russia and the United States to fight both groups would in effect strengthen Assad's position, and could undermine US efforts to press him to agree a negotiated political settlement to the civil war.