North Korea has fired four banned ballistic missiles over 620 miles, with three of them landing in waters which Japan claims as its exclusive economic zone, officials said.

Military sources said the missiles flew some 1,000 km (539 nautical miles), and were launched from the area of Tongchang-ri - where a missile base is located - in a possible retaliation by North Korea to joint US and South Korean drills that began last week.

According to local news sites, an unnamed ministry official warned the projectiles could be intercontinental ballistic missiles capable of reaching the US mainland.

However, Pentagon spokesman Navy Captain Jeff Davis said on Monday that the United States saw no indications of an intercontinental ballistic missile launch.

The U.S. military did, however, leave open the possibility of additional North Korean ballistic missile launch attempts beyond the four that landed in the sea off northwest Japan.

North Korea leader Kim Jong Un at the Sohae Satellite Launching Station in Cholsan County, North Pyongan Province, for the testing of a new engine for an intercontinental ballistic missile

The Defense Ministry said the missiles flew about 539 nautical miles after being launched from Tongchang-ri (Sohae Satellite Launching Station). Three of the missiles fell within Japan's exclusive economic zone (pictured in light blue), 188 miles to 215 miles west of the Oga Peninsula in Akita Prefecture

'There were four that landed. There may be a higher number of launches that we're not commenting on. But four landed and splashed in the Sea of Japan,' Navy Captain Jeff Davis, a Pentagon spokesman, told a news briefing.

The four missiles were fired from North Pyongan province around 7:36 am South Korean time, the South Korean ministry said in a statement, adding they landed in the East Sea, also known as the Sea of Japan.

Japanese Prime Minister Shinzo Abe said Tokyo lodged a 'strong protest' to North Korea after the reclusive state launched the four ballistic missiles, three of which fell into Japan's Exclusive Economic Zone.

'The latest launches of ballistic missiles clearly demonstrate evidence of a new threat from North Korea,' Abe told reporters at his residence.

Moscow is seriously worried about North Korea's latest missile drills, Kremlin spokesman Dmitry Peskov said on Monday.

'Definitely, we are seriously worried - these are the sort of actions that lead to a rise in tension in the region and of course in this situation, traditionally, Moscow calls for restraint from all sides,' Peskov told a conference call with reporters.

The European Union has also condemned North Korea for firing the four banned ballistic missiles and said it would consult with Japan and international partners on how to react.

EU foreign affairs chief Federica Mogherini said launches were 'in utter disregard' of several U.N. resolutions and further raised tension in the region.

A PAC-3 surface-to-air missile launcher is seen in position on the grounds of the defence ministry in Tokyo on March 6, 2017.Japan's Prime Minister Shinzo Abe said three of the four missiles North Korea launched landed in Japanese-controlled waters

A member of Japan Self-Defense Force stands by a PAC-3 Patriot missile unit deployed against the North Korea's missile firing, at the Defense Ministry in Tokyo, Monday, March 6, 2017

She says North Korea needs to return to a dialogue with the international community and immediately halt plans for more such missile launches.

The missile launches came as Seoul and Washington launch annual joint military exercises, infuriating Pyongyang which condemns them as provocative rehearsals for invasion.

Visiting a North Korean army headquarters unit, leader Kim Jong-Un ordered the troops to 'set up thorough countermeasures of a merciless strike against the enemy's sudden air assault', the state-run Korean Central News Agency said on the day the Foal Eagle exercises started last week.

North Korea fired a ballistic missile last month - its first such launch since October - which Seoul had said was aimed at drawing 'global attention' to its nuclear and missile programme and 'testing the response from the new US administration' of President Donald Trump.

U.S. Army soldiers prepare their military exercise in Paju, near the border with North Korea, South Korea, Monday, March 6, 2017. North Korea fired missiles in an apparent reaction to huge military drills by Washington and Seoul that Pyongyang insists are an invasion rehearsal

A television displays news broadcast's infographics reporting on North Korea test-firing ballistic missiles, at a station in Seoul, South Korea, on Monday

North Korea is barred under UN resolutions from any use of ballistic missile technology.

But six sets of UN sanctions since Pyongyang's first nuclear test in 2006 have failed to halt its drive for what it insists are defensive weapons.

The South's Joint Chief of Staff said in a statement that Monday's launch was made in the Tongchang-ri area in North Pyongan province.

The area is the home of the North's Seohae Satellite Station, where it has conducted prohibited long-range rocket launches in recent years.

While it was not immediately clear what was fired, Pyongyang has staged a series of missile test-launches of various range in recent months.

Last year the country conducted two nuclear tests and numerous missile launches in its quest to develop a nuclear weapons system capable of hitting the continental US.

Leader Kim Jong Un is pushing for a nuclear and missile program that can deter what he calls U.S. and South Korean hostility toward the North.

Pictured is a satellite image take in 2013 of the Sohae Satellite Launching Station in Cholsan County, North Pyongan Province

North Korea is barred under UN resolutions from any use of ballistic missile technology