U.S. Deputy Secretary of Defense William Lynn says North Korea's missiles could threaten the continental United States if the communist nation’s missile program continues to progress.

Lynn made the remark during a Senate hearing Wednesday, agreeing with an assessment by Senator John McCain that the U.S. should be prepared for a "worst-case scenario" with Pyongyang.

At the hearing, Pentagon officials claimed the North is working with Iran and Syria to develop ballistic missiles.