A U.S. military expert says North Korea continues to develop intercontinental ballistic missiles that could carry nuclear warheads. He also warned that Washington's ability to defend itself against such missiles remains limited.

U.S. Missile Defense Agency Director Henry Obering told a U.S. Senate hearing that Pyongyang's development and export of ballistic missiles remains a major concern.

Obering, whose agency is affiliated with the U.S. Defense Department, said North Korea's new short- and medium-range missiles could boost the precision and mobility of its military.

Separately, senior Defense Department official Charles McQueary said that in missile defense tests last September, a U.S. interceptor successfully downed a target missile. But McQueary, the department's chief weapons tester, also warned that current capabilities are limited. He called for repeated, more precise tests to ward off North Korea's missile threat against the United States.