Vladimir Putin is preparing to attack Isil in Syria amid growing signs that Western leaders may support a Russian plan to allow Bashar al-Assad to remain in power in the country.
Russia has sent dozens of fighter jets and helicopter gunships to Syria as he steps up his support for Assad, the country's president, in the fight against Isil jihadists.
Mr Putin is understood to have told America that he is prepared to authorise unilateral Russian airstrikes on Isil targets if the US does not back his plans to take on the jihadists while allowing Assad to remain in power.
There have been growing signs that Western leaders are now softening their opposition to Assad remaining in power.
Angela Merkel, the German Chancellor, said on Thursday: "We have to speak with many actors. This includes Assad, but others as well.
"Not only with the United States of America, Russia, but with important regional partners, Iran, and Sunni countries such as Saudi Arabia."
And Recep Tayyip Erdogan, the Turkish President, who has been a fierce critic of Assad, on Thursday suggested for the first time that the Syrian president could have a role to play in a future political transition.
"The process could possibly be without Assad, or the transitional process could be with him," he said.
However, there was also concern amongst European leaders about Russia's decision to increase its military presence in Syria.
Mr Putin has drafted a request for the Russian upper house of parliament to approve the deployment of 2,000 air personnel to Syria, but has yet to formally submit it, according to Bloomberg, citing anonymous sources.
Mr Putin's spokesman denied the claim.
Last night, Iranian President Hassan Rouhani said Tehran was not in a coalition with Russia to fight Isil militants in the Middle East and that ties with the United States had improved, though there was "still a long road to travel."
Speaking through an interpreter, Mr Rouhani said Mr Putin told him personally that Moscow wants to play a more active role in combatting extremist groups in the region.
"I do not see a coalition between Iran and Russia on fighting terrorism in Syria," Mr Rouhani, in New York for the United Nations General Assembly, told a group of senior editors from media organisations.
He noted improvements in US-Iranian relations but cautioned that it was unclear when ties between the two long-estranged nations could return to normal.
"The situation has certainly changed," Rouhani said. "We can point to the tangibles, the many steps forward, but there is still a long road to travel."
He described the historic nuclear deal between Iran and the United States, Britain, France, Germany, Russia and China as a "big test" for US-Iranian relations and said that it was important to create an atmosphere of trust.
Michael Fallon, Britain's Defence Secretary, said that the "Russian build-up in Syria only complicates an already complicated and difficult situation".
And Jean-Yves Le Drian, the French Defence Minister, called on Moscow to justify a "very significant" buildup in Syria and said if its intention was "to protect" Mr Assad, it should say so.
Russia's increasing involvement in Syria is likely to dominate next week's session of the United Nations General Assembly in New York, where Mr Putin is scheduled to meet US President Barack Obama on Monday.
Russia has called on Western and Middle Eastern countries to form a broad anti-Isil coalition including Mr Assad's government, arguing that Syrian government forces are the only ones capable of combatting terrorists on the battlefield.
Mr Putin is a staunch ally of Mr Assad and has supplied him with weapons and military advice throughout the four-year civil war.
But a recent increase in Russian activity in Syria, including reported deployment of drones and combat aircraft to an airbase near the government stronghold of Latakia, has prompted speculation that Russia is preparing to intervene on the regime's side in the conflict.
The developments have raised concerns about the dangers of uncoordinated operations by both Russian forces and the Nato-led coalition currently prosecuting a campaign against Isil. (© Daily Telegraph, London)