The launch came as Japanese Foreign Minister Takeshi Iwaya visited South Korea for a series of meetings with top officials, with the Asian neighbours seeking to boost bilateral ties before Trump returns to office next week.

"The South Korean military detected several short-range ballistic missiles fired into the East Sea," the military in Seoul said, referring to the body of water also known as the Sea of Japan.

South Korean and US intelligence agencies had monitored Pyongyang's launch preparations, the military said, with Seoul maintaining "full readiness" and sharing information with Washington and Tokyo.

Tuesday's launch took place around 9:30 am (0030 GMT) near North Korea's Ganggye area, with the missiles flying 250 kilometres (155 miles) before landing in the sea, according to the military.

The United States Indo-Pacific Command condemned the test, calling on North Korea "to refrain from further unlawful and destabilising acts".

Seoul's acting president Choi Sang-mok also slammed the launch, saying it violated UN Security Council resolutions.

"Seoul will respond more strongly to North Korea's provocations based on its strong security posture and alliance with the US," he said.

Experts said the latest launch could be intended as a message to the incoming US president.

"It may indicate an intention to put pressure ahead of the Trump administration's second term," said Yang Moo-jin, president of the University of North Korean Studies in Seoul.

- Second test this month -

Ahn Chan-il, a defector-turned-researcher who runs the World Institute for North Korea Studies, told AFP the test launch "appears to be an intention to assert presence ahead of the Trump administration".

He said it could also be aimed at "destabilising South Korea during Seoul's own period of turmoil". Suspended President Yoon Suk Yeol's impeachment trial over his failed martial law bid began on Tuesday.

Tuesday's launch was Pyongyang's second this month after it fired what it said was a new hypersonic missile system last week.

The location of the test site was undisclosed but images released by North Korean state media KCNA showed leader Kim Jong Un observing last week's launch with his teenage daughter Ju Ae.

KCNA cited the use of a "new compound of carbon fibre" in the missile's engine, which experts warned could allow Pyongyang to hit further targets with technology to which only the United States, Russia and China currently have access.

Relations between the two Koreas have been at one of their lowest points in years, with the North launching a flurry of ballistic missiles last year in violation of UN sanctions.

In response to Pyongyang's increased capabilities, South Korea's state arms procurement agency said on Tuesday it has begun developing a new missile defence system "aiming to intercept North Korea's nuclear and missile threats at higher altitudes".

The missile system will cost 567.7 billion won ($388 million) and is scheduled to be ready by 2028, Seoul's Defense Acquisition Program Administration (DAPA) said in a statement.

- Pyongyang's ties with Moscow -

Last week's alleged hypersonic missile launch came as US Secretary of State Antony Blinken was visiting South Korea.

Blinken said during that visit that Moscow was increasing cooperation with Pyongyang, adding they were working ever more closely on advanced space technology.

Ahn said another reason for Tuesday's launch may be the testing of "missiles for export to Russia to be used in Ukraine".

North Korea test-fired in late October what it said was its most advanced and powerful solid-fuel intercontinental ballistic missile (ICBM). It then fired a salvo of short-range ballistic missiles days later.

US and South Korean intelligence also believe that North Korea started in October to send thousands of troops to fight against Ukraine and has since suffered hundreds of casualties.

However, neither North Korea nor Russia has officially confirmed that Pyongyang's forces are fighting for Moscow.