BRUSSELS (AFP) - Nato on Tuesday condemned North Korea's "irresponsible" nuclear test as a flagrant breach of United Nations resolutions and a grave threat to international security.

"We condemn in the strongest terms the test by North Korea," the United States-led military alliance said. "This irresponsible act, along with the December missile launch, poses a grave threat to international and regional peace, security and stability."

The test and North Korea's pursuit of weapons of mass destruction amounted to "continued defiance" of the international community, it said.

"We call on the North Korean authorities to cease immediately such provocative actions, to meet their obligations under international law and to comply fully with the decisions of the international community," it added.