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A giant offshore crane salvages the South Korean ship Cheonan in April. The ship sank March 26. ((Choi Jae-ku/Associated Press))

North Korea says it must bolster its nuclear capability to cope with a "hostile" U.S. policy amid high tension over the deadly sinking of a South Korean warship.

An international investigation concluded last month that North Korea torpedoed the warship Cheonan near the tense Korean sea border, killing 46 sailors.

North Korea denies the allegation and has warned that punishment could trigger war.

"The recent disturbing development on the Korean Peninsula underscores the need for (North Korea) to bolster its nuclear deterrent in a newly developed way to cope with the U.S. persistent hostile policy toward (the North) and military threat toward it," the North's Foreign Ministry said Monday in a release.

The statement, carried by the official Korean Central News Agency, didn't elaborate on how North Korea would strengthen its nuclear capability.

North Korea cites the threat of a nuclear attack from the U.S. as a main reason behind its drive to build atomic weapons. Pyongyang, which is believed to have enough weaponized plutonium for at least a half-dozen weapons, conducted its first nuclear test in 2006, drawing international condemnation and UN sanctions.

G8 condemns nuclear program

The warning came after top world leaders at a G8 meeting in Huntsville, Ont., on Saturday criticized North Korea over its nuclear program. The leaders also condemned the attack that led to the sinking of the Cheonan but didn't explicitly blame North Korea for it.

Backed by the U.S. and other countries, South Korea has taken its own punitive measures against North Korea, including trade restrictions.

The North reacted angrily, declaring it was cutting off ties with Seoul and threatening to attack.

South Korea has taken the issue to the UN Security Council to seek punishment for North Korea.