As concerns build that an influx of Russian military aid to Syria could make the conflict there worse, U.S. Secretary of State John Kerry spoke Tuesday with his Russian counterpart Sergei Lavrov.
The U.S. Defense Department has said Moscow appears to be setting up an air base near the northwestern Syrian port of Latakia.
At the White House, Press Secretary Josh Earnest repeated the U.S. position that Russia's support of Syrian President Bashar al-Assad is a "losing bet."
"The reason for that is we have seen over the years that because of his failed leadership and because of his willingness to slaughter innocent people using the mechanics of that country’s military, he has lost the legitimacy to lead that country," Earnest said.
"We have made clear that the solution - despite the decision of Russians to build up their military - the solution in Syria requires a diplomatic strategy."
Earnest indicated President Barack Obama might phone Russia's President Vladimir Putin in the coming days.
Russian newspaper Vedomosti, citing a source close to Russia's Defense Ministry, reported Tuesday that Russian personnel are simply helping to repair and upgrade infrastructure at a Syrian airfield in Latakia and at the Russian navy's supply and maintenance facility at Tartus, farther south on the coast, its only base on the Mediterranean.
In a Russian television interview aired on Sunday, Foreign Minister Lavrov confirmed that Moscow is supplying and will continue to supply weapons to Syria's government. Addressing concerns over a build up of Russian personnel, he said the shipments are "inevitably accompanied by Russian specialists, who help to get the appropriate equipment up and running [and] to train Syrian personnel in the handling of these weapons."
Yet some observers in Moscow say Russian personnel in Syria are engaged in something more significant than routine repair work and training.
Alexander Shumilin, head of the Center for Analysis of Middle East Conflicts at the Institute for U.S. and Canada Studies in Moscow, said he is convinced Russia's actions are aimed at ensuring the physical survival of President Assad and his inner circle.
"The emphasis is on the survival of the president, not maintaining his power ... in Damascus," Shumilin told VOA's Russian service. "Because Assad is losing territory to the advancing enemies, and it cannot be ruled out that he will have to hide somewhere in the north, in the district of Latakia, if events on the battlefield [continue to] unfold in the same way."
This is why, according to Shumilin, facilities are being strengthened in Latakia district, a stronghold of Assad's Alawite co-religionists.
"Correspondingly, while Bashar Assad is still alive and has not yet been overthrown, it should be possible to start a political process of handing over power," he said. "Because only Assad can ensure Russia's role in this transition. With his departure, this role will sharply decrease."
In an interview with VOA Russian service, Mahmoud al-Hamza, a Moscow-based member of the Syrian National Council, a coalition of opposition groups, also argued Russia's behavior in Syria is aimed at preventing Assad from being toppled.
"Apparently, it is motivated by a desire to transfer Assad ... to Latakia and keep him there as the legitimate president of Syria," Hamza said, adding that if Assad's government falls, Russia "will lose virtually everything" it has in Syria.
"That's why they are rushing to gain a foothold on the coast, above all to help the Alawites and preserve their interests," he said, adding: "I don't think this is happening without coordination with Iran."
In Hamza's view, Moscow's intervention in Syria is only adding to the crisis. "There will be more war, blood, and the chances for a political solution will disappear. In Russia, they say all the time that the Syrians must solve their own problems" he said. "Why, then, do they choose to intervene, and so unceremoniously?"
Yet the Institute for U.S. and Canada Studies's Shumilin argued Moscow is inclined to carry out a purely defensive operation, not an offensive one.
"It is not a matter of helping Assad to regain control of the country," he said. "At least, no one in Moscow has declared such intentions."
Shumilin thinks Moscow's actions in Syria may also be providing a diversion from its controversies elsewhere. "The Kremlin would like to shift attention from the impasse in Ukraine to its actions in Syria," he said.
As a bonus, Shumilin added, the actions in Syria play well to the militaristic fever that has gripped a significant part of Putin's electorate for more than a year.
VOA's Aru Pande contributed to this report from the White House