The Pentagon is considering sending U.S. troops to fight beside Iraqi soldiers as they take on more complex missions in the battle against Islamic State militants, according to Gen. Martin Dempsey, the nation's top military officer.

American ground troops may have to help Iraqi forces if they move to recapture critical areas, including Mosul, Iraq's second largest city, from the Sunni extremists,  Dempsey told a congressional hearing Thursday.

"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 U.S. forces, but we're certainly considering it," he told the House Armed Services Committee.

Dempsey is chairman of the Joint Chiefs of Staff.

President Obama has vowed not to reintroduce ground troops to Iraq, but Dempsey's comments - echoing those he made in September - suggest that option remains a possibility under some circumstances.