The chairman of the U.S. Joint Chiefs of Staff has expressed concern that North Korea might follow its torpedoing of a South Korean warship with other provocative acts.

Admiral Mike Mullen told "Fox News Sunday" that North Korean leader Kim Jong-il tends not to stop after a single provocative move and that he worries Kim could be planning something else.

Mullen said the political, diplomatic and international focus to keep the situation stable in Northeast Asia is absolutely vital.

When asked whether North Korea could go back on the State Department’s list of nations that sponsor terrorism based on a U.N. report last week showing the North exported weapons to Iran, Mullen said the decision is up to President Barack Obama and the U.S. leadership.