U.S. Assistant Secretary of State-designate Kurt Campbell says the U.S. will not accept a nuclear North Korea.

Speaking at his Senate confirmation hearing Wednesday, Campbell said he is prepared to pursue bilateral and trilateral discussions with South Korea and Japan to reaffirm that the U.S. and its allies will not accept North Korea as a nuclear state.

He added that Washington remains firm in its defense of its partners in the East Asian region against, what he called, “the direct and reckless challenges” posed by the North.

Campbell, a former U.S. deputy assistant secretary of defense, also stressed the need to further strengthen U.S. cooperation with both South Korea and Japan.

If confirmed, Campbell would replace top nuclear negotiator Christopher Hill, who was named by President Barack Obama to the key post of ambassador to Iraq.