Story Highlights• NEW: U.S. intelligence says activity observed around nuclear test site
• NEW: U.S. to raise issue before U.N. Security Council
• Japanese PM said international community would "respond harshly"
• Pyongyang insists weapons are only for defensive purposes
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UNITED NATIONS (CNN) -- North Korea, citing American belligerence and pressure, said Tuesday it will conduct a nuclear test.
The North Korean Foreign Ministry issued the comment in a statement published by the Korean Central News Agency, or KCNA, the communist country's official news agency.
"The field of scientific research of the DPRK (North Korea's official name) will in the future conduct a nuclear test under the condition where safety is firmly guaranteed," the statement said. (Watch why North Korea may want to test a nuclear bomb -- 3:37)
A date and time for the test was not issued.
A U.S. intelligence source said movement of people, vehicles and equipment has been observed around the North's nuclear test site in recent days and weeks.
A U.S. State Department spokesman said any North Korea nuclear tests would be "an unacceptable threat to peace and stability in Asia and the world."
"The U.S. will continue to work with its allies and partners to discourage such a reckless action and will respond appropriately," State Department spokesman Sean McCormack said.
U.S. Ambassador to the U.N. John Bolton said he plans to raise the issue before the U.N. Security Council, calling it "a possible test case for the council to engage in preventative diplomacy."
"It is a test of the Security Council. It is a test of how the council responds," Bolton said.
Japanese Prime Minister Shinzo Abe said Tuesday that if North Korea proceeded with a nuclear test, "the international community would respond harshly."
"Any form of nuclear testing by North Korea would be unacceptable," he said.
Japanese Foreign Minister Taro Aso said Pyongyang had followed through on threats before.
South Korea raised its security level after the announcement, news services reported.
It is the first time North Korea has made an official announcement that it is going to conduct nuclear tests. Previously, it said it had the right to conduct such tests.
"The U.S. extreme threat of a nuclear war and sanctions and pressure compel the DPRK to conduct a nuclear test, an essential process for bolstering nuclear deterrent, as a corresponding measure for defense," the Foreign Ministry said.
Six-party talks on the country's nuclear program have stalled, and North Korea test-fired missiles in July. There have been attempts to get the talks back on track.
North Korea wants bilateral talks with the United States before the six-party talks resume and it wants Washington to ease up on economic pressures.
"The DPRK's nuclear weapons will serve as reliable war deterrent for protecting the supreme interests of the state and the security of the Korean nation from the U.S. threat of aggression and averting a new war and firmly safeguarding peace and stability on the Korean peninsula under any circumstances."
At the same time, North Korea said it would back "nuclear non-proliferation as a responsible nuclear weapons state" and do all it can "to realize the denuclearization of the peninsula and give impetus to the world-wide nuclear disarmament and the ultimate elimination of nuclear weapons."
"The ultimate goal of the DPRK is not a 'denuclearization' to be followed by its unilateral disarmament but one aimed at settling the hostile relations between the DPRK and the U.S. and removing the very source of all nuclear threats from the Korean Peninsula and its vicinity," the statement said.
The country said it "officially announced that it manufactured up-to-date nuclear weapons after going through transparent legitimate processes to cope with the U.S. escalated threat of a nuclear war and sanctions and pressure. The already declared possession of nuclear weapons presupposes the nuclear test."
The country said it would "never use nuclear weapons first but strictly prohibit any threat of nuclear weapons and nuclear transfer."
CNN's Sohn Jie-Ae contributed to this report