Seoul says North Korea carried out missile tests

North Korea has fired four ballistic missiles into the sea off Japan's northwest coast, South Korean and Japanese officials said, days after the reclusive state promised retailiation over US-South Korea military drills it sees as a preparation for war.

Seoul said four missiles were fired from North Pyongan province into the East Sea on Monday and that South Korea and the United States were "closely analysing" tracking data for further details.

Seoul and Washington began annual joint military exercises last week - something North Korea has long condemned as a deliberate provocation.

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 (370km) from its coast.

"This clearly shows North Korea has entered a new stage of threat," Abe said in parliament.