SEOUL, South Korea » The top U.S. military officer says South Korea could see more North Korean provocations as Pyongyang to strengthen leader Kim Jong Il’s successor.

Adm. Mike Mullen told reporters Thursday that North Korea’s "threat remains very real."

The chairman of the U.S. Joint Chiefs of Staff says North Korea has shown no signs of slowing its pursuit of nuclear weapons.

He’s urging North Korean ally China to play a "leadership role" in restraining Pyongyang.

North Korea is building up Kim Jong Il’s third son and heir-apparent Kim Jong Un.

Mullen’s visit comes amid high tension between the Koreas. Seoul says two North Korean attacks last year killed 50 South Koreans.