"This became ground zero for jihadists around the world," he said in an interview with CBS's 60 Minutes,
according to an excerpt aired by the network on Sunday.
This "gave them some traditional military capacity and not just terrorist capacity," Mr. Obama said, adding that it was "absolutely true" that the U.S. overestimated the ability and willingness of the new Iraqi government to push back against Islamic State.
But the near-term plan was to destabilize Islamic State.
The full 60 Minutes interview is slated to air Sunday evening.
"We've been clear that there will not be a U.S. ground invasion of Iraq or Syria," he said. He left the door open, however, to the idea that a no-fly zone could be established over Syria at some point.
On ABC News "This Week," House Speaker John Boehner (R., Ohio) indicated that sending in American combat troops could become necessary to eliminate the Islamic State threat.
"At some point, somebody's boots have to be on the ground," Mr. Boehner said. So far the White House and its allies have deployed airstrikes against the militants and are preparing to train pro-Western Syrian rebels to fight on the ground.
"Maybe we can get enough of these forces trained and get them on the battlefield," Mr. Boehner said.