US ready for 'targeted action' against Iraq insurgents
But he stressed "American forces will not be returning to combat in Iraq".
He said that up to 300 military advisers would be sent to help the Iraqi government's efforts.
However, he stressed that the crisis could only effectively be solved through political means.
He said it was not the US's place to choose Iraq's leaders, but urged them to pursue an "inclusive agenda".
That may be seen as a veiled criticism of Shia Prime Minister Nouri Maliki, who has been accused of anti-Sunni policies which have helped inflame unrest, correspondents say.
BBC