The Pentagon's top general has admitted that the US may be required to send ground troops into Iraq to retake the key city of Mosul from the Islamic State [IS].
General Martin Dempsey, the chairman of the Joint Chiefs of Staff, made the warning in a briefing to Congress on the campaign to destroy the terror group.
"I'm not predicting, at this point, that I would recommend that those forces in Mosul and along the border would need to be accompanied by US forces, but we're certainly considering it," General Dempsey said.
He added that it was "not in our interests to take this fight on ourselves with a large military contingent".
His comments come after US President Barack Obama ruled out "boots on the ground" in a combat role in Iraq.
Despite the pledge to not send combat troops into Iraq, Obama has doubled America's presence in the country with an extra 1,500 trainers and advisers to aid the Iraqi army.
The White House is now hoping that a $5.6bn (£3.57bn) package to finance the fight against the terror group next year will be approved.
Following reports that IS's leader Abu Bakr al-Baghdadi had been killed in a US airstrike in Iraq, the group released an audio message purportedly from the world's most wanted terrorist, in which he called for jihadists to carry out attacks against Muslim Shi'ites and Westerners.
"Dismember their limbs; snatch them as groups and individuals," he says. "Erupt volcanoes of jihad everywhere".
He also announces "the expansion of the Islamic State to new lands" - including Saudi Arabia, Yemen, Egypt, Libya and Algeria - where he says local Islamist groups have pledged their alliance to the "caliphate".