SEOUL (AP): North Korea test-launched a suspected intercontinental ballistic missile and two shorter-range weapons into the sea Wednesday, South Korea said, hours after President Joe Biden ended a trip to Asia where he reaffirmed the US commitment to defend its allies in the face of the North's nuclear threat.

If confirmed, it would be North Korea's first ICBM launch in about two months amid stalled nuclear diplomacy with the United States. Breaking its 2018 moratorium on long-distance launches, North Korea in March claimed to have test-launched its longest-range missile as part of its development of functioning nuclear-armed missiles that can reach the American homeland.

The launches took place as North Korea made a much-disputed claim that its first domestic COVID-19 outbreak was weakening.

After an emergency national security council meeting, the South Korean government said North Korea fired a suspected ICBM and two short-range ballistic missiles.

North Korea's sustained provocations can only result in stronger and faster South Korea-US combined deterrence and can only deepen North Korea's international isolation, the South Korean government statement said. (Our) government is maintaining constant readiness to strongly and effectively respond to any kind of North Korean provocation.

South Korea's military said the suspected ICBM reached a maximum height of 540 kilometers while traveling 360 kilometers east after being fired from the North's capital region.

The Joint Chiefs of Staff said the North apparently lost the second missile 20 kilometers into flight, while the third missile flew 760 kilometers on an apogee of 60 kilometers.

A JCS statement said the US and South Korean militaries fired two surface-to-surface missiles in response to demonstrate the allies' striking capabilities. It said the allies had detected North Korea's preparations for the launches in advance. It said South Korea's air force on Tuesday conducted an elephant walk involving 30, fully armed F-15K fighter jets parading along a runway in formation.

The US Indo-Pacific Command earlier said the missile launches highlight the destabilizing impact of (North Korea's) illicit weapons programme though they didn't pose an immediate threat to US territory and its allies. A command statement said the US commitment to the defense of the South Korea and Japan remains ironclad.

The White House said Biden has been briefed on the North Korean missile launches and will continue to be briefed as information develops.

Japanese Defence Minister Nobuo Kishi said the launches were an act of provocation and absolutely impermissible. He accused North Korea of pressing ahead with its weapons development programme while ignoring the people's suffering amid the spread of the coronavirus in the country.

The launches were North Korea's 17th round of missile firings this year. Experts have said the launches show North Korea's determination to move ahead with its push to modernise its weapons arsenals despite the COVID-19 outbreak and apply more pressure on its rivals to wrest sanctions relief and other concessions amid dormant nuclear diplomacy.

US, South Korean and Japanese officials have said North Korea could soon conduct its first nuclear test in nearly five years as well.

North Korea's unusual pace in weapons tests this year included an ICBM launch in March that was its first since 2017. North Korea described that launch as a demonstration of its biggest missile, the Hwasong-17.

However, South Korea's military said the North instead may have fired a smaller ICBM. Whichever it was, the missile flew longer and higher than any other weapon the North has ever tested and had the potential range to reach the entire US mainland, experts say.

After their summit in Seoul on Saturday, Biden and Yoon said they would consider expanded military exercises to deter North Korean nuclear threats.

Before Wednesday, North Korea's most recent missile tests were May 12, hours after the country acknowledged a COVID-19 outbreak and ended a widely disputed claim to have been coronavirus-free for more than two years.