North Korea has fired an unidentified ballistic missile into the sea off South Korea's east coast, Seoul's military said on Monday, the latest in an apparent volley of tests by Pyongyang this year.

"North Korea has fired an unidentified missile into the East Sea," South Korea's Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.

Tokyo also confirmed the launch, with the Japanese defence ministry saying "a suspected ballistic missile was launched from North Korea" in a post on X, formerly Twitter.

Japan's coast guard, citing the defence ministry, said shortly after the initial announcement that the missile appeared to have already fallen.

Japanese media including public broadcaster NHK reported that the suspected missile fell outside Japan's Exclusive Economic Zone, citing unnamed government sources.

Seoul-based specialist site NK News said that the "brief flight time, likely under ten minutes, points to the launch involving a short-range ballistic missile (SRBM) or 600mm multiple launch rocket system (MLRS)."

The latest launch comes after UN sanctions monitoring against the nuclear-armed nation was upended last month by Russia.

Pyongyang's ally Moscow in March used its United Nations Security Council veto to effectively end UN monitoring of violations of the raft of sanctions on Kim Jong Un's government for its nuclear and weapons programme.

On Friday, North Korea tested a "super-large warhead" designed for a strategic cruise missile, state media said, with Seoul's military confirming it had detected cruise missile launches around the same time.

Unlike their ballistic counterparts, the testing of cruise missiles is not banned under current UN sanctions on North Korea.

Cruise missiles tend to be jet-propelled and fly at a lower altitude than more sophisticated ballistic missiles, making them harder to detect and intercept.

Analysts have warned that North Korea could be testing cruise missiles ahead of sending them to Russia for use in Ukraine, with Washington and Seoul claiming Kim has shipped weapons to Moscow, despite UN sanctions banning any such moves.

Seoul claims Pyongyang has sent around 7,000 containers of weapons to Moscow for use in Ukraine.

The largely isolated country has recently bolstered military ties with Moscow, and this month it thanked Russia for its veto blocking the renewal of a panel of UN experts that monitored international sanctions against it.

It has also ramped up testing, claiming in early April to have tested a new medium-to-long-range solid-fuel hypersonic missile.

This year, Pyongyang has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

Last year, the North conducted a record number of missile tests in defiance of UN sanctions in place since 2006 and despite warnings from Washington and Seoul.

Pyongyang declared itself an "irreversible" nuclear weapons state in 2022.

US Secretary of State Antony Blinken, who was in Seoul last month, will be back in the region this week making his second visit in less than a year to China.