That assessment comes despite public assertions by President Barack Obama and top aides that Putin has embarked on an ill-conceived mission in support of Syrian President Bashar al-Assad that it will struggle to afford and that will likely fail, according to Reuters.

Five U.S. officials interviewed by Reuters concurred with the view that the Russian mission has been mostly successful so far and is facing relatively low costs.

Since its campaign began on September 30, Russia has suffered minimal casualties and, despite domestic fiscal woes, it is managing to cover the operation's cost, which analysts estimate at $1-2 billion a year. The war is being funded from Russia's regular annual defense budget of about $54 billion, a U.S. intelligence official said, according to the report.

Moscow has repeatedly claimed that its intervention is aimed at stabilizing the Assad government and helping it fight the Islamic State group, though Western officials and Syrian opposition groups say its air strikes mostly have targeted moderate rebels.