The early-morning launch came as the UN Security Council met in New York to discuss last week's test of what Pyongyang called a hypersonic missile, though Seoul has cast doubt on that claim.

But the South Korean military said the "suspected ballistic missile" launched Tuesday had reached hypersonic speeds -- a sign of "progress" from last week's test.

In the decade since leader Kim Jong Un took power, North Korea has seen rapid advances in its military technology at the cost of international sanctions.

Tuesday's missile landed outside Japan's exclusive economic zone. While there were no immediate reports of damage, Japan's Prime Minister Fumio Kishida called the launch "extremely regrettable".

The United States condemned what it called a "ballistic missile launch", and reaffirmed its commitment to defend both South Korea and Japan.

"This launch is in violation of multiple UN Security Council Resolutions and poses a threat to the DPRK's neighbors and the international community," the department said, using the abbreviation of North Korea's official name.

"We remain committed to a diplomatic approach to the DPRK and call on them to engage in dialogue."

The missile, fired towards the sea east of the peninsula on Tuesday at around 7:27 am (2227 GMT Monday), flew 700 kilometres (435 miles) at an altitude of around 60 kilometres (37 miles) at Mach 10 speed, Seoul's Joint Chiefs of Staff said.

Hypersonic missiles travel at speeds of Mach 5 and higher and can manoeuvre mid-flight, making them harder to track and intercept.

The UN Security Council meeting to discuss Pyongyang's weapons programs came after six countries, including the US and Japan, called on North Korea to "engage in meaningful dialogue towards our shared goal of complete denuclearization".

Pyongyang had likely planned the latest launch to coincide with the UN meeting "to maximise its political impact," Shin Beom-chul, a researcher at the Korea Research Institute for National Strategy, told AFP.

He said the Tuesday launch looked like a hypersonic missile test, judging by the purported speed, but warned against reading too much into it.

"Since South Korea claimed [the January 5 test] wasn't a hypersonic missile referring to the speed, Pyongyang may have tried to showcase its maximum speed," this time around, he said.

Hypersonic missiles were listed among the "top priority" tasks for strategic weapons in its current five-year plan, and it announced its first test -- of the Hwasong-8 -- in September last year.

Pyongyang has also said it had successfully tested new submarine-launched ballistic missiles, a long-range cruise missile, and a train-launched weapon in 2021.

- No talks -

The new tests come as North Korea has refused to respond to US appeals for talks.

At a key meeting of North Korea's ruling party last month, Kim vowed to continue building up the country's defence capabilities, without mentioning America.

Instead of the policy positions on diplomacy, for which Kim's New Year statements are closely watched, he focused on food security and economic development.

Dialogue between Washington and Pyongyang remains stalled and the country is under multiple sets of international sanctions over its nuclear and ballistic missile programmes.

The impoverished nation has also been under a rigid self-imposed coronavirus blockade that has hammered its economy.