John Kerry and Sergei Lavrov at meeting in Vienna on Syria
John Kerry and Sergei Lavrov at meeting in Vienna on SyriaReuters
US Secretary of State John Kerry on Monday said he hoped it was "very possible, even likely" he would hold talks on Syria with Russian counterpart Sergei Lavrov.

Washington and Moscow have been in contact for weeks over establishing military cooperation to fight the Islamic State jihadist group in Syria.

"We are indeed engaged currently in ongoing conversations that have been going on now for several weeks and it is my hope that we are reaching the end of those discussions one way or the other," Kerry told reporters during a visit to Kenya.

"In the next days, our teams will meet, this week, and depending on where those discussions go, it is very possible, even likely, that Foreign Minister Lavrov and I would meet," he said.

"But that decision has to be made on the basis of where we are in the next couple of days."

He added: "It is possible that something could be agreed at upon before the end of the month but I can't tell you whether it's likely. I wouldn't express optimism -- I would express hope."

Russia and the United States back opposing sides in Syria's five-year war, which has left 280,000 people dead and forced half the population to flee their homes.

Successive rounds of international negotiations to end the war, which erupted in 2011 after President Bashar al-Assad's regime unleashed a brutal crackdown against a pro-democracy revolt, have so far failed.

Russian planes have also been carrying out raids on Syrian rebel groups, some of which are supported by the United States.

US and allied forces, meanwhile, have been striking IS -- a target that Russia, separately, says it too pounding.

Last Tuesday and Wednesday Russia struck at IS from a base in western Iran, which is also an ally of Syria.

But Iran on Monday said that Russian raids from its territory were "a specific, authorised mission and it's over for now."

Kerry, asked about this development, declined to comment.

"On Russia, and bombings, and Iran, you'd have to ask the Iranians and the Russians why they made whatever decision they made to something that I'm not sure anybody had admitted previously was in fact going on," the secretary of state said.