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SEOUL, March 7 (Reuters) - North Korean leader Kim Jong Un supervised the test launches of four missiles by an army unit commissioned with attacking U.S. military bases in Japan, the country's official news agency reported on Tuesday, stepping up threats against Washington as its troops conduct joint military exercises with South Korea.
North Korea fired four ballistic missiles into the sea off Japan's northwest on Monday, angering South Korea and Japan, days after it promised retaliation over the military drills which it sees as preparation for war.
"Involved in the drill were Hwasong artillery units of the KPA Strategic Force tasked to strike the bases of the U.S. imperialist aggressor forces in Japan in contingency," the North's official KCNA news agency said.
"In the hearts of artillerymen ... there was burning desire to mercilessly retaliate against the warmongers going ahead with their joint war exercises," KCNA said.
"He (Kim) ordered the KPA Strategic Force to keep highly alert as required by the grim situation in which an actual war may break out any time, and get fully ready to promptly move, take positions and strike so that it can open fire to annihilate the enemies."
The missiles North Korea fired on Monday were unlikely to have been intercontinental ballistic missiles (ICBM), South Korea said, which can reach the United States. They flew on average 1,000 km (620 miles) and reached an altitude of 260 km (160 miles).
Some landed as close as 300 km (190 miles) from Japan's northwest coast, Japan's Defence Minister said earlier.
The United States and Japan have requested a United Nations Security Council meeting on the launches, which will likely be scheduled for Wednesday, diplomats said.
North Korea had threatened to take "strong retaliatory measures" after South Korea and the United States began the annual drills on Wednesday to test defensive readiness against possible aggression from the North.
North Korea criticises the drills and has previously conducted missile launches to coincide with them.
(Reporting by Ju-min Park and Jack Kim; Editing by Lincoln Feast and James Dalgleish)