MUNICH - The Syrian opposition leader met Russia's foreign minister on Saturday and a diplomatic source said he would also see Iran's foreign minister, opening a window to a possible breakthrough in efforts to broker an end to Syria's civil war.

Russia and Iran have been the staunchest allies of Syrian President Bashar al-Assad throughout an armed uprising against his rule, and any understandings they might reach with Assad's foes could help overcome the two sides' refusal to negotiate.

At an annual international security conference in Munich, Syrian National Coalition leader Moaz Alkhatib had talks with Russia's Sergei Lavrov that may have been made possible by Alkhatib signalling readiness to talk to Damascus.

He also met separately with US Vice President Joe Biden and UN special envoy for Syria Lakhdar Brahimi.

"Russia has a certain vision but we welcome negotiations to alleviate the crisis and there are lots of details that need to be discussed," Alkhatib said after the meeting.

A diplomatic source said the Alkhatib would also meet Iranian Foreign Minister Ali Akbar Salehi, who was attending the Munich security conference on Saturday, but this could not be independently confirmed.

Russia has blocked three UN Security Council resolutions aimed at pushing out Assad out or pressuring him to end the civil war, in which more than 60,000 people have died. But Moscow has also tried to distance itself from Assad by saying it is not trying to prop him up and will not offer him asylum.

"The talks about Syria are intensifying and the Iranians have been drawn in. Let's see how it all ends," the diplomatic source said, speaking on condition of anonymity.

"BIG SIGNAL"

Alkhatib put his authority within the opposition movement at risk earlier this week when he broke ranks to say he would be willing to meet Syrian officials to discuss a transition if political prisoners arrested during the uprising were freed.

The opposition coalition's 12-member politburo then told Alkhatib not to respond to any proposals made in Munich without consulting with them first, with one opposition source citing concern that Alkhatib's move would damage the revolt's morale.

Outgoing US Secretary of State Hillary Clinton praised Alkhatib's apparent readiness to meet Assad envoys outside Syria, calling him "not only courageous but smart".

She also voiced concern that Iran had recently increased military support for Assad.

While some headway was apparently being made in Munich, Iranian media said that Saeed Jalili of Iran's Supreme National Security Council had travelled to Damascus to meet officials and help Assad "stand against plots hatched by global arrogance" - an allusion to the United States and other Western powers.

A comment by Russian Prime Minister Dmitry Medvedev this week that Assad's chances of staying in power were getting "smaller and smaller" was regarded in some quarters as a sign of a shift in the Kremlin's Syria policy.

At the same time, Syrian opposition figure Hassan Bali, in Munich as an independent observer, called Alkhatib's meeting with Biden "a big signal from the Americans" that they were upgrading support for rebels fighting to topple Assad.

Biden said in Munich that although there was still no international agreement, nobody could doubt "the increasingly desperate plight of the Syrian people and the responsibility of the international community to address that plight".

There was little evidence at the Munich conference that the US and Russian positions on Assad were getting any closer.

"The persistence of those who say that priority number one is the removal of Assad is the single biggest reason for the continuing tragedy in Syria," Lavrov told the conference.

Biden on the other hand said the White House was "convinced that President Assad, a tyrant hell-bent on clinging to power, is no longer fit to lead Syrian people and he must go".

Russia is Assad's main arms supplier and, with Iran, has been among his strongest supporters during the 22-month-old conflict, which began with peaceful protests and evolved into civil war after Assad tried to crush unrest by military force.

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