Russia may allow a resolution of the Syrian civil war which would see Syrian President Bashar Assad out of power, according to U.S. and Russian officials, and Syrian opposition leaders, Bloomberg reported on Monday.

According to the officials, Russia, the U.S., Saudi Arabia and Syrian opposition leaders have been discussing plans for sidelining Assad since at least June, Bloomberg said.

According to Bloomberg, the sides have been considering a plan which would see Assad retaining a ceremonial role as interim head of state ahead of future elections. Russia is Assad's longtime ally, and has resisted previous proposals which sought to oust the Syrian president. According to the officials, this change in Russia's stance is due to the rise of Islamic State.

“There’s a convergence on the threat of ISIS,” Vice President of the Middle East Institute in Washington Paul Salem told Bloomberg. “This convergence wasn’t there when they last tried diplomacy two years ago.”

However, Russian President Vladimir Putin's spokesman, Dmitry Peskov told Bloomberg that "only the Syrian people can decide the fate of Syria, not some outside countries."

Last week it was reported that Moscow sent an advanced anti-aircraft missile system to Syria, as part of what the West believes is increased military support for embattled Assad. The Western officials said the SA-22 system would be operated by Russian troops, rather than Syrians. It was on its way to Syria but had not yet arrived.

Lebanese sources have told Reuters, meanwhile, that Russian troops have begun participating in combat operations on behalf of the Assad government. Moscow has not commented on those reports. Speaking at a news conference in Moscow, Russian Foreign Minister Sergei Lavrov said Russia was sending military equipment to Syria to help the Assad government combat Islamic State fighters, and had sent experts to help train the Syrian army to use it.

An ally of Damascus since the Cold War, Moscow maintains its only Mediterranean naval base at Tartous on the Syrian coast, and protecting it would be a strategic objective.