Russia and other big powers have told mediator Kofi Annan they support his idea of a Syrian national unity cabinet, diplomats said Wednesday.

Annan's proposal for a political transition aimed at ending the 16-month conflict in Syria is one of the main topics that Russia, the other four permanent Security Council members and key players in the Middle East will discuss at a meeting in Geneva on Saturday, the envoys told Reuters on condition of anonymity.

One diplomat summarized Annan's proposal, saying the Syria conflict can only end when all sides see a peaceful way to a shared future. Annan made clear it was vital that (any) settlement (be) irreversible, (with) clear transition steps in fixed timeline, he said.

These include establishing a transitional national unity government to create a neutral backdrop for transition, the diplomat said in his summary of Annan's plan.

It could comprise present government members, opposition and others, but would need to exclude those whose continued participation or presence would jeopardize the transition's credibility, or harm prospects for reconciliation and stability.

The diplomat added that the idea of excluding certain people was clearly referring to Syrian President Bashar al-Assad, though Annan's proposal does not explicitly say Assad could not serve in a national unity government. That gives Russia the option of insisting that Assad be allowed to stay in power.

The Russians signaled to Annan that they accept his transition plan, he said. Several Western diplomats confirmed his remarks, adding that all five permanent veto-wielding U.N. Security Council members backed it.

Annan earlier this week gave the parties to the talks a few days to respond to a set of recommendations entitled On Guidelines and Principles of a Syrian-led transition. By late Tuesday, the Russians had accepted the paper in full, including language that spells out Assad's departure, three officials, who all were informed of the decision, told Bloomberg. 

Russia has realized that Assad is losing the battle to preserve his grip on power, the U.N. officials said, and now the government of President Vladimir Putin is seeking a leading role in paving a smooth exit for Moscow's longtime client and arms customer.

When Assad went into total war footing, he lost the Russians, George Lopez, a former U.N. sanctions investigator who's now at the Kroc Institute for International Peace Studies at the University of Notre Dame in Indiana, told Bloomberg.

But another diplomat said Russia's acceptance of Annan's proposal, which he circulated to the five permanent Security Council members this week, did not mean it has abandoned Assad.

I'm very skeptical, he said. I don't see the Russians giving up on Assad.

The Russian mission at the United Nations was not available for comment.