North Korea's foreign ministry says the country will conduct a nuclear test to bolster its defenses against what it calls U.S. hostility.
The official Korean Central News Agency said the nuclear test will take place "in the future," but did not specify a date.
In response, U.S. Secretary of State Condoleezza Rice said any nuclear test by North Korea would be a "very provocative act."
The Japanese and British governments said such a test would result in serious consequences. The European Union said today that the announcement is an "irresponsible and escalatory step" that increases tension and undermines regional stability.
South Korea said it has strengthened its security level and alert status as a result of the North Korean statement.
But the Russian foreign ministry cast doubts on the threat, saying North Korea has made similar claims before.
North Korea has long maintained that it has a nuclear arsenal, but observers say no known tests have been conducted.
Pyongyang says U.S. pressure has "compelled" North Korea to test one of its nuclear devices.
In its statement, North Korea said it would never use nuclear weapons first, and it called for a Korean peninsula free of nuclear weapons.
North Korea says financial sanctions Washington has imposed on North Korea are adversely affecting the country's security.