BRUSSELS (Reuters) - NATO condemned North Korea's nuclear weapon test on Tuesday, calling it an "irresponsible act" that posed a grave threat to world peace.

North Korea's pursuit of weapons of mass destruction represented continued defiance of the U.N. Security Council, the North Atlantic Council, made up of NATO ambassadors, said in a statement.

"This irresponsible act, along with the December missile launch, poses a grave threat to international and regional peace, security and stability," it said, urging North Korea to "cease immediately such provocative actions".

(Reporting by Adrian Croft; Editing by Justyna Pawlak)