South Korea's military on Sunday claimed that North Korea today launched a ballistic missile that flew about 700 kilometers.
The latest missile launch comes just days after the election of a new South Korean president and is seen a direct challenge to him.
The move also coincided with the US, Japanese and European militaries gathering for war games in the Pacific.
Confirming the early morning launch, South Korea's Joint Chiefs of Staff said, "The North fired this morning an unidentified projectile from Kusong, North Pyongan province," but had few other details, including what type of ballistic missile was fired.
A statement added that the South Korean and US militaries are analysing the details.
The kind of projectile matters because while North Korea regularly tests shorter-range missiles, it is also working to master the technology needed to field nuclear-tipped missiles that can reach the US mainland.
The Trump administration has called such North Korean efforts unacceptable and has swung between threats of military action and offers to talk as it formulates a policy.
The launch also comes as troops from the U.S., Japan and two European nations gather on remote U.S. islands in the Pacific for drills that are partly a message to North Korea. The USS Carl Vinson, an aircraft supercarrier, is also engaging with South Korean navy ships in waters off the Korean Peninsula, according to Seoul's Defense Ministry.
Last week South Koreans elected a new president, Moon Jae-in, who favors a much softer approach to the North than his conservative predecessors, Park Geun-hye, who is in jail awaiting a corruption trial.
Moon called an emergency national security meeting Sunday, but he didn't immediately make any statement on the launch.
North Korea needs tests to perfect its missile program, but it also is thought to time its launches to come after the elections of new US and South Korean presidents in what analysts say are efforts meant to gauge a new administration's reaction.
Japanese Chief Cabinet Secretary Yoshihide Suga said the missile flew about 800 kilometers (500 miles) from a launch site on North Korea's western coast for about 30 minutes and landed in the Sea of Japan, but not inside Japan's exclusive economic zone. Prime Minister Shinzo Abe told reporters Sunday that the launch, which is banned by the United Nations, is "absolutely unacceptable" and that Japan will respond resolutely.
While Pyongyang regularly tests shorter-range missiles, it is also working to master the technology needed to field nuclear-tipped missiles that can reach the U.S. mainland. Past North Korean missiles have flown farther than 800 kilometers (500 miles) in tests, landing closer to Japan, but this launch follows a series of high-profile failures.
North Korea's past satellite rocket launches have been called clandestine tests of ICBM technology, but it is not believed to have tested a true intercontinental ballistic missile yet. The Trump administration has called North Korean ballistic and nuclear efforts unacceptable and has swung between threats of military action and offers to talk as it formulates a policy.
The North's state media said Saturday it will bolster its nuclear capability unless the United States abandons its hostile policy.
"The United States should never expect us to give up our nuclear capability," the main Rodong newspaper said in a commentary carried by the Korean Central News Agency. It said U.S. President Donald Trump's "maximum pressure and engagement" policy is only aimed at "stifling us" and will compel the North to "strengthen our nuclear deterrent at the maximum speed."
The White House today described a ballistic missile test by North Korea as a provocative behaviour and called for stronger sanctions against Pyongyang.
"Let this latest provocation serve as a call for all nations to implement far stronger sanctions against North Korea," White House Press Secretary Sean Spicer said in a statement.
The US Pacific Command detected and tracked a North Korean missile launch at approximately 10:30 AM (Hawaii time) Saturday.
"With the missile impacting so close to Russian soil - in fact, closer to Russia than to Japan - the President cannot imagine that Russia is pleased," Spicer said.
"North Korea has been a flagrant menace for far too long. South Korea and Japan have been watching this situation closely with us," he said.
He said the US maintains its ironclad commitment to stand with its allies in the face of the serious threat posed by North Korea.
(With AP agencies)