Russian forces appear to be expanding their military presence in Syria through the development of two additional bases that pose new challenges for the Obama administration as it struggles to avert a clash with Moscow in the Middle East.

Private satellite images released Tuesday revealed new construction at two Syrian military facilities near the Mediterranean coast, the latest sign Russia is preparing to inject its military forces into the country’s 4½-year war.

While U.S. military officials assessed the importance of the projects and overall buildup, the Obama administration is seeking to transform the potential showdown into a fresh diplomatic initiative to push Syrian President Bashar al-Assad—Russia’s longtime ally—from power, senior administration officials said.

Specifically, officials are exploring whether the U.S. could work with Moscow to ease Mr. Assad from power and pave the way for a successor from his Alawite sect, preventing a collapse of the government and a likely takeover by Islamic extremists, a senior administration official said Tuesday.