The trip to a US base on the edge of the inter-Korean buffer zone came as a South Korean navy boat fired warning shots at North Korean fishing vessels which intruded over a tense sea border in the Yellow Sea.

The incursion, which fueled security jitters in South Korea, comes nearly eight months into a stand-off over North Korea's nuclear weapons drive.

Pyongyang fired a barrage of shrill warnings at Seoul and Tokyo last week, accusing the allies of supporting Washington's tough stance against the Stalinist country.

Wolfowitz is to visit Japan Monday after talks with South Korean officials to exchange views on the nuclear crisis.