CAIRO (Reuters) - A nuclear test by North Korea would pose an "unacceptable threat" to peace and stability in the world and further isolate the reclusive nation, the U.S. State Department said on Tuesday.

A statement from the North Korean Foreign Ministry released earlier said Pyongyang would conduct its first nuclear test and blamed a U.S. "threat of nuclear war and sanctions" for forcing its hand.

"It would be a very provocative act by the North Koreans," Secretary of State Condoleezza Rice said at a news conference with Egyptian Foreign Minister Ahmed Aboul Gheit.

"A North Korean nuclear test would ... create a qualitatively different situation on the Korean peninsula," she said, saying other countries in the region would likely reassess their dealings with Pyongyang if it conducted a test.

After the United States last year began cracking down on Pyongyang's offshore bank accounts, North Korea refused to return to six-party talks with China, Japan, Russia, South Korea and the United States that are designed to persuade Pyongyang to abandon its nuclear ambitions in exchange for economic and political benefits.

"A North Korea test would severely undermine our confidence in the North Koreans' commitment to six-party talks and would pose an unacceptable threat to peace and stability in Asia and the world," State Department spokesman Sean McCormack said.

"A provocative action of this nature would only further isolate the North Korean regime and deny the people of the North the benefits they so rightly deserve," he added. "The U.S. will continue to work with its allies and partners to discourage such a reckless action and will respond appropriately."

U.S. officials declined to say how they might respond.

Reuters