Russia has sent a military advance team to Syria and is taking other steps that the United States fears may signal that President Vladimir V Putin is planning to vastly expand his military support for President Bashar al-Assad, administration officials said onFriday.
The Russian moves, including the recent transport of prefabricated housing units for hundreds of people to a Syrian airfield and the delivery of a portable air traffic control station there, are another complicating factor in Secretary of State John Kerry's repeated efforts to enlist Putin's support for a diplomatic solution to the bloody conflict in Syria.
The Russians have also filed military overflight requests with neighboring countries through September.
American officials acknowledge that they are not certain of Russia's intentions, but some say the temporary housing suggests that Russia could deploy as many as 1,000 advisers or other military personnel to the airfield near the Assad family's ancestral home. The airfield serves Latakia, Syria's principal port city.
Other American officials say they see no indication that Russia intends to deploy significant numbers of ground forces, but they say the housing would enable Russia to use the airfield as a major hub for ferrying in military supplies for the Syrian government, or possibly as a launching pad for Russian airstrikes in support of President Assad's forces.
American intelligence analysts are also looking at ship loadings in Russia to determine what might be bound for Syria.
Syria is one of Russia's major arms clients, and is also host to a Russian naval base at the port city Tartus. But the new concerns from intelligence analysts, as well as news and social media reports in the Middle East, led to warnings this week from the State Department and White House about Putin's intentions.
''We have regularly and repeatedly expressed our concern about Russian military support for the Assad regime,'' said John Kirby, the State Department spokesman. ''But we're also watching their actions very carefully. If these reports are borne out, it would represent a very serious shift in the trajectory of the Syria conflict and call into question any Russian commitment to a peaceful settlement.''
Kerry flew to Sochi, Russia, in May to meet with Putin to explore whether the two sides could cooperate on Syria. In August, Kerry followed up with an unusual three-way meeting in Qatar on the Syria crisis with Sergey V. Lavrov, the Russian foreign minister, and their Saudi counterpart, Adel al-Jubeir.
Stepped-up Russian military support for the Syrian government could pose a problem for the United States in several ways. If Putin's intention is to support not just the Syrian government but also Assad, that could undercut Kerry's contention that the Syrian president needs to leave power as part of any political solution to the conflict. And if Russian pilots carried out airstrikes, administration officials say, the choice of targets might further aggravate the growing chaos.