At a White House news conference, Obama frequently assailed Russian President Vladimir Putin, who he accused of acting out of a position of weakness to defend a crumbling, authoritarian ally.
Friday prayers were canceled in insurgent-held areas of Syria's Homs province hit by Russian warplanes this week, with residents concerned that mosques could be targeted, according to one person from the area.
Putin's decision to launch strikes on Syria marks a dramatic escalation of foreign involvement in a more than four-year-old civil war in which every major country in the region has a stake.
It also gives fuel to domestic critics of Obama who say his unwillingness to act on Syria has allowed Moscow to stage its biggest show of force in the Middle East in decades.
But the U.S. president warned that Russia and Iran, Assad's main backer in the Muslim world, have isolated the majority of Syrians and angered their Sunni Muslim neighbors.
"An attempt by Russia and Iran to prop up Assad and try to pacify the population is just going to get them stuck in a quagmire and it won't work," Obama said. (+ video) » | Alistair Bell and Tom Perry | Washington/Moscow | Saturday, October 3, 2015
