BEIRUT – Syria’s most powerful ally and protector, Russia, began positioning itself Thursday for the fall of President Bashar Assad, saying for the first time that rebels might overthrow him and preparing to evacuate thousands of Russian citizens from the country.

The head of NATO echoed the Russian assessment, saying the Syrian government is near collapse following a nearly two-year conflict that has killed more than 40,000 people and threatened to ignite the Middle East.

Assad appears to be running out of options, with insurgents at the gates of the capital and the country fracturing under the weight of a devastating civil war.