Nuclear-armed North Korea launched four ballistic missiles on Monday in another challenge to U.S. President Donald Trump, with three landing provocatively close to America’s ally Japan, AFP reported.

This comes after, Seoul and Washington began annual joint military exercises last week that always infuriate Pyongyang, with the North’s military warning of “merciless nuclear counter-action”.

Under leader Kim Jong-Un, Pyongyang has ambitions to develop an intercontinental ballistic missile (ICBM) capable of reaching the U.S mainland — which Trump has vowed will not happen, according to the AFP report.

Seoul said four missiles were fired from Tongchang County, North Pyongan province into the East Sea — its name for the Sea of Japan — and that South Korea and the US were “closely analyzing” tracking data for further details.

The missiles travelled around 1,000 kilometres and reached an altitude of 260 kilometres, said a spokesman for South Korea’s Joint Chiefs of Staff, adding they were unlikely to be ICBMs.

Japanese Prime Minister Shinzo Abe said three of the North Korean missiles came down in Tokyo’s Exclusive Economic Zone (EEZ) — waters extending 200 nautical miles from its coast.

“This clearly shows North Korea has entered a new stage of threat,” Abe told parliament.

The North’s repeated launches “clearly violate UN Security Council resolutions”, he said. “We can never tolerate this.”

Tokyo’s chief government spokesman Yoshihide Suga added that Japan was considering calling for an emergency Security Council meeting.

Pyongyang carried out two atomic tests last year and a series of missile launches, but Monday was only the second time.

In Washington, the State Department strongly condemned the launches, saying the US was ready to “use the full range of capabilities at our disposal against this growing threat”.

“We remain prepared — and will continue to take steps to increase our readiness — to defend ourselves and our allies from attack,” acting spokesman Mark Toner said in a statement.