North Korea on Tuesday (May 31) appeared to have tried and failed with a fresh ballistic missile launch in violation of existing UN resolutions, South Korea's Defence Ministry said.
The UN measures ban North Korea from any use of ballistic missile technology, although it regularly fires short-range missiles into the sea off its east coast.
The defence ministry in Seoul said the missile test took place at around 5.20am (4.20am, Singapore time) near the eastern port city of Wonsan.
"The attempted missile launch ... is believed to have failed," a ministry spokesman said.
"We are analysing and closely monitoring the situation and maintaining a watertight defence posture," he added.
The ministry declined to speculate on the type of missile, but the South's Yonhap news agency quoted military sources saying it was understood to be a medium-range Musudan missile.
Tensions have been running high on the divided Korean peninsula since the North's fourth nuclear test in January, followed by a long-range rocket launch the following month.
'IN A RUSH'
Tuesday's attempted launch appears to have been its first missile test since then, and experts have said it was unusual to test-fire a missile so soon after a previous failure.
The South Korean military said Pyongyang's continuous missile launches could stem from Kim's order in March for further tests of nuclear warheads and ballistic missiles.
"They must've been in a rush. Maybe Kim Jong Un was very upset about the failures," said Lee Choon-geun, senior research fellow at South Korea's state-run Science and Technology Policy Institute.
And in recent weeks Pyongyang has voiced anger at Seoul's refusal to accept repeated offers of military talks to de-escalate the situation.
"We are tracking signs that North Korea is preparing a ballistic missile test and are maintaining combat readiness," a defence ministry official told AFP.
In April the North tried and failed three times to test-fire a powerful new mid-range missile known as a Musudan.
JAPANESE MILITARY ON ALERT
In Tokyo, public broadcaster NHK said the Japanese government had put its military on alert for a possible launch, with orders to intercept any missile that threatened Japanese territory.
Under the order, the Self-Defence Forces will deploy Aegis destroyers equipped with missile interceptors offshore and PAC-3 surface-to-air anti-ballistic missiles, NHK said.
"We have no reports of any damage in Japan. We are gathering and analysing data. The defence ministry is prepared to respond to any situation," Japanese Minister of Defence Gen Nakatani told a media briefing.
"North Korea shows no sign of abandoning the development of nuclear missiles and so we will continue to work closely with the U.S. and South Korea in response and maintain a close watch on North Korea," Nakatani said.
The Musudan is believed to have a range of anywhere between 2,500 and 4,000 kilometres. The lower range covers the whole of South Korea and Japan, while the upper range would include US military bases on Guam.
The missile has never been successfully flight-tested.
The three failures in April were seen as an embarrassment for the leadership, coming ahead of a party congress which was meant to celebrate the country's achievements.
During the congress, North Korean leader Kim Jong-Un personally extended the offer of military dialogue with the South.
The proposal was repeated several times by the North's military, but Seoul dismissed all the overtures as insincere "posturing" given Kim's vow at the same congress to push ahead with the country's nuclear weapons programme.