Russia does not see keeping Bashar al-Assad in power as a matter of principle, the Foreign Ministry in Moscow has said in comments that suggested a divergence of opinion with Iran, the Syrian president's other main international backer.

Fuelling speculation of Russian-Iranian differences over Assad, the head of Iran's Revolutionary Guard Corps suggested Tehran may be more committed to him than Russia, saying Moscow "may not care if Assad stays in power as we do".

While Russia and Iran have been Assad's foremost foreign supporters during Syria's four-year-old war, the US, its Gulf allies and Turkey have insisted the president must step down as part of any eventual peace deal.

Talks in Vienna on Friday among the main foreign players involved in diplomatic efforts on Syria failed to reach agreement on Assad.

Asked if saving Assad was a matter of principle for Russia, Russian Foreign Ministry spokeswoman Maria Zakharova said: "Absolutely not, we never said that."

"We are not saying that Assad should leave or stay."

But another regime change in the Middle East could be a catastrophe that "could simply turn the whole region into a large black hole", she added.

Ms Zakharova said Russia had not changed its policy on Assad and that his fate should be decided by the Syrian people.

But her remarks appeared to suggest a difference of approach compared with Iran, which has sent forces to fight alongside Assad's military and ordered in fighters from the Lebanese Hezbollah group, which it controls.

Syria's deputy foreign minister rejected the idea of a transitional period sought by Western states that want Assad removed from power, saying during a visit to Iran that an expanded government was being discussed.

"We are talking about a national dialogue in Syria and an expanded government and a constitutional process. We are not at all talking about what is called a transitional period," Faisal Mekdad said.

Russia intervened militarily at the end of September to support Assad by launching bombing raids on rebel groups trying to overthrow him.

But Moscow has also shown increasing flexibility as it steps up diplomatic efforts to resolve a conflict that has killed 250,000 and displaced millions.

Syrian government officials and members of the country's splintered opposition could meet in Moscow next week.

Moscow's goal was not to support Assad, but to save the Syrian state and defeat terrorist groups, a Russian analyst said. "It is the beginning of a political process," said Irina Zvyagelskaya, a Middle East analyst at the Russian Academy of Sciences.

Russian Foreign Minister Sergei Lavrov will meet UN Syria envoy Staffan de Mistura in Moscow on Wednesday to discuss attempts to start a dialogue between Damascus and the opposition, Moscow's foreign ministry said.

At the talks in Vienna, where Russia was the leading player, Moscow said it wanted opposition groups to participate in future discussions on the Syria crisis and exchanged a list of 38 names with Saudi Arabia.

The list included mostly former and current members of the National Coalition for Syrian Revolutionary and Opposition Forces (SNC), Syria's Western-backed political opposition bloc.