WASHINGTON (Reuters) - Planning is underway for the military campaign to liberate Mosul from Islamic State, Brett McGurk, U.S. President Barack Obama's special envoy in the fight against Islamic State said on Tuesday.

"Mosul will be a significant military challenge but also a political, diplomatic and humanitarian challenge. The planning is now underway," McGurk told a U.S. Senate Foreign Relations Committee hearing.

(Reporting by Yara Bayoumy and Patricia Zengerle; Writing by Yara Bayoumy; Editing by Jeffrey Benkoe)