North Korean leader Kim Jong Un supervised the test launches of four missiles by an army unit commissioned with attacking US military bases in Japan, the country’s official news agency reports.

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 US-South Korea military drills it sees as preparation for war.

Meantime North Korea’s UN ambassador, Ja Song-nam, said in a letter to the UN Security Council on Monday the US was using nuclear-propelled aircraft carries, nuclear submarines, nuclear strategic bombers and stealth fighters in the joint exercises that began on March 1.

“It may go over to an actual war,” he warned of the military drills.

“Consequently, the situation on the Korean Peninsula is again inching to the brink of a nuclear war.”

The US and Japan have requested an urgent meeting of the UN Security Council on the launches.

A spokesman for Nikki Haley, US ambassador to the United Nations, said the request for a meeting was made in coordination with South Korea. No date for the meeting has been set.

North Korea on Monday launched four ballistic missiles that fell into the sea 300 to 350 kilometres off the coast of Japan.

A US State Department spokesman was quoted as saying North Korea had violated UN Security Council resolutions explicitly prohibiting it from launches using ballistic missile technology.

The spokesman, Mark Toner, also said the US State Department was “prepared to use the full range of capabilities at our disposal against this growing threat.”

Japanese Prime Minister Shinzo Abe said Toyko had lodged a “stern protest” with Pyongyang.

Three of the missiles fell into Japan’s exclusive economic zone, creating “a grave threat to our country’s national security,” a government spokesman said.

China has condemned the launch and urged calm in the region.