The launch came three days after North Korea fired two short-range ballistic missiles into the sea. The North also flight-tested a pair of purported long-range cruise missiles on Tuesday.
North Korea on Sunday fired what appeared to be the most powerful missile it has tested in the past five years, possibly breaching a self-imposed suspension as it attempts to wrest concessions from Washington and neighbours amid a prolonged stalemate in diplomacy.
Sunday's test was the North's seventh round of weapons launches this month. The unusually fast pace of tests indicates North Korea's intent to pressure the Biden administration over long-stalled nuclear negotiations.
Meanwhile, pandemic-related difficulties further shocked the North Korean economy, broken by decades of mismanagement and crippling US-led sanctions over its nuclear weapons program.
The Japanese and South Korean militaries said the missile was launched on a lofted trajectory, apparently to avoid the territorial spaces of neighbours, and reached a maximum altitude of 2,000 kilometres, travelling 800 kilometres before landing in the sea.
The flight details suggest the North tested its longest-range ballistic missile since 2017, when it twice flew intermediate-range ballistic missiles over Japan and separately flight-tested three intercontinental-range ballistic missiles, demonstrating the potential to reach deep into the American homeland.
South Korean President Moon Jae-in called an emergency National Security Council meeting. He described the test as a possible "midrange ballistic missile launch" that brought North Korea to the brink of breaking its 2018 suspension in testing nuclear devices and longer-range ballistic missiles.
Japanese defence minister Nobuo Kishi told reporters it was clear that the missile was the longest-range weapon the North has tested since launching its Hwasong-15 ICBM in November 2017.
The launch came after North Korean leader Kim Jong Un chaired a ruling party meeting on 20 January, where senior party members made a veiled threat to lift the moratorium, citing what they perceived as US hostility and threats.
In April 2018, Kim declared that "no nuclear test and intermediate-range and inter-continental ballistic rocket test-fire" were necessary for the North any longer as he pursued diplomacy with then-US president Donald Trump in an attempt to leverage his nukes for badly needed economic benefits.
In his most substantial comments toward the North in years, Moon said the situation around the Korean Peninsula is beginning to resemble 2017 when North Korea's provocative run in nuclear and long-range missile testing resulted in a verbal exchange of war threats between Kim and Trump.
Moon described the North's latest tests as a violation of UN Security Council resolutions and a "challenge toward the international society's efforts to denuclearise the Korean Peninsula, stabilise peace and find a diplomatic solution" to the nuclear standoff.
According to his office, the North "should stop its actions that create tensions and pressure and respond to the dialogue offered by the international community, including South Korea and the United States," Moon said.
Moon, who had ambitiously pushed for inter-Korean engagement, held three summits with Kim in 2018 while also lobbying to set up Kim's first summit with Trump in 2018, where they issued vague aspirational goals for a nuclear-free Korean Peninsula without describing when and how it would occur.
Upping the ante before Beijing Olympics
But the diplomacy derailed after the collapse of the second Kim-Trump meeting in 2019 when the Americans rejected North Korea's demand for significant sanctions relief in exchange for a partial surrender of its nuclear capabilities.
Japanese chief cabinet secretary Hirokazu Matsuno said Sunday's missile flew for around 30 minutes and landed in waters outside Japan's exclusive economic zone. There were no immediate reports of damage to boats or aircraft.
The US Indo-Pacific Command said the US condemns North Korea's testing activity and calls on the North to refrain from further destabilising acts. It said the latest launch did not "pose an immediate threat to US personnel, territory, or that of our allies."
The launch came three days after North Korea fired two short-range ballistic missiles into the sea.
On Tuesday, the North also flight-tested a pair of purported long-range cruise missiles while vowing to strengthen its nuclear "war deterrent" and build more powerful weapons.
Experts say the North could halt its testing spree after the start of the Beijing Winter Olympics next week out of respect for China, its major ally and economic lifeline.
But there are also expectations that the North could significantly up the ante in weapons demonstrations once the Olympics end in February to grab the attention of the Biden administration, which has been focusing more on confronting China and Russia over its conflict with Ukraine.
"North Korea is launching a frenzy of missiles before the start of the Beijing Olympics, mostly as military modernisation efforts. Pyongyang also wants to boost national pride as it gears up to celebrate political anniversaries in the context of economic struggles," said Leif-Eric Easley, a professor at Ewha University in Seoul.
"It wants to remind Washington and Seoul that trying to topple it would be too costly. By threatening stability in Asia while global resources are stretched thin elsewhere, Pyongyang is demanding the world compensate it to act like a 'responsible nuclear power,'" Easley added.
North Korea has justified its testing activity as an exercise of its rights to self-defence and threatened more decisive action after the Biden administration imposed fresh sanctions following two tests of a purported hypersonic missile earlier this month.
While desperate for outside relief, Kim has shown no willingness to surrender the nuclear weapons and missiles he sees as his strongest guarantee of survival.
Analysts say Kim's pressure campaign aims to force Washington to accept the North as a nuclear power and convert their nuclear disarmament-for-aid diplomacy into negotiations for mutual arms reduction.
Kim last year announced a new five-year plan for developing weapons and issued an ambitious wish list that included hypersonic weapons, spy satellites, solid-fuel intercontinental ballistic missiles and submarine-launched nuclear missiles.
State media said Friday that Kim visited an unspecified munitions factory producing a "major weapons system," and that the workers pledged loyalty to their leader who "smashes with his bold pluck the challenges of US imperialists and their vassal forces".