North Korea conducted what is thought to be its largest intercontinental ballistic missile (ICBM) test ever on Thursday, militaries in South Korea and Japan said, marking a dramatic end to a self-imposed moratorium on long-range testing.

It would be the first full-capability launch of the nuclear-armed state's largest missiles since 2017, and represents a major step in the North's development of weapons that might be able to deliver nuclear warheads anywhere in the United States.

The North's return to major weapons tests also poses a new national security headache for U.S. President Joe Biden as he responds to Russia's invasion of Ukraine, and presents a challenge to South Korea's incoming conservative administration.

Japanese authorities said the launch appeared to be a "new type" of ICBM that flew for about 71 minutes to an altitude of about 6,000km (3,728 miles) and a range of 1,100km (684 miles) from its launch site.

It landed inside Japan's exclusive economic zone (EEZ), 170 km (106 miles) west of the northern prefecture of Aomori, at 3:44 p.m. (0644 GMT), the coast guard said.

South Korea's Joint Chiefs of Staff put the missile's maximum altitude at 6,200km and its range at 1,080km.

That is further and longer than North Korea's last ICBM test in 2017, when it launched a Hwasong-15 missile that flew for 53 minutes to an altitude of about 4,475km and range of 950km.

Thursday's ICBM launch prompted South Korea to test fire a volley of its own, smaller ballistic and air-to-ground missiles to demonstrate it has the "capability and readiness" to precisely strike missile launch sites, command and support facilities, and other targets in North Korea if necessary, South Korea's Joint Chiefs of Staff said in a statement.

South Korean deputy national security advisor Suh Choo-suk condemned the launch as "a clear violation of U.N. Security Council resolutions, and a reversal of the moratorium on ICBM launches, which North Korea had promised to the international community."

South Korea's JCS said the latest missile was launched from near Sunan, where Pyongyang's international airport is located. On March 16, North Korea launched a suspected missile from that airport that appeared to explode shortly after liftoff, South Korea's military said.

NEW ICBM?

U.S. and South Korean officials have warned recently that North Korea had been preparing to test fire its largest ICBM yet, the Hwasong-17.

U.S. officials said at least two recent tests, on Feb. 27 and March 5, featured the Hwasong-17 system, but did not demonstrate full ICBM range or capability.

Pyongyang did not identify the missile system used in those launches, but said they were testing components for a reconnaissance satellite system.

This month, leader Kim Jong Un said North Korea would soon launch multiple satellites to monitor military movements by the United States and its allies.

Thursday's launch would be at least the 11th North Korean missile test this year, an unprecedented frequency that has drawn condemnation from the United States, South Korea and Japan.

Analysts say the Hwasong-17 is "considerably larger" than the Hwasong-15. It was first unveiled in October 2020 and displayed a second time in October 2021.

The missile, which has been shown on a transporter vehicle with 11 axles, would be one of the world's largest road-mobile ICBMs.

'SERIOUS PROGRESS'

Amid a flurry of diplomacy in 2018, Kim declared a self-imposed moratorium on testing ICBMs and nuclear weapons, but suggested the North could resume such testing amid stalled denuclearisation talks.

That moratorium had often been touted as a success by former U.S. President Donald Trump, who held several historic summits with Kim in 2018 and 2019, but never gained a concrete pact to limit the North's nuclear or missile arsenals.

On Jan. 19, North Korea said it would bolster its defences against the United States and consider resuming "all temporally suspended activities", according to state news agency KCNA, an apparent reference to the self-imposed moratorium.

New construction has also been spotted at North Korea's only known nuclear test site, which was shuttered in 2018.

The looming prospect of possible nuclear tests, more joint U.S.-South Korea military drills, and the new conservative South Korean president mean "all conditions are present for a tit-for-tat chain reaction of escalatory steps," said Chad O'Carroll, CEO of Korea Risk Group, which monitors North Korea.

"Though Biden would prefer to focus exclusively on the Ukraine crisis, it's likely he will soon face crisis-level tensions between the Koreas," he said.

With the sanctions regime at an impasse at the U.N. Security Council and North Korea opposed to talks on denuclearisation for the foreseeable future, Pyongyang is now likely capable of making serious progress on its weapons development programme with little risk of substantive punishment, O'Carroll added.