Syrian government forces, US officials said, are too few, too poor and too weak to secure the country. Islamic State, and other militants in Syria, have ample opportunity to regroup, especially if the political grievances that drove the conflict remain unresolved, the officials said.
"We think the Russian declarations of ISIS' defeat are premature," a White House National Security Council spokeswoman said. "We have repeatedly seen in recent history that a premature declaration of victory was followed by a failure to consolidate military gains, stabilize the situation, and create the conditions that prevent terrorists from reemerging".
Marine Major Adrian Rankine-Galloway, a Pentagon spokesman, said the United States had not observed any significant withdrawal since Putin's announcement.
Although he did not predict future moves, he said: "There have been no meaningful reductions in combat troops following Russia's previous announcements planned departures from Syria."