North Korea has reportedly test-launched two Musudan mid-range ballistic missiles, Washington and Seoul military sources say.
"The North launched one missile presumed to be Musudan from areas near Wonsan at around 5:58 am, but it is assumed to be unsuccessful," said the South Korean Joint Chiefs of Staff on Tuesday.
The launch was also confirmed by the US Pacific Command’s Navy Commander Dave Benham.
According to South Korea sources, a second missile assumed to be a Musudan was also launched, the outcome of which is yet to be determined.
Earlier in the day, Japan put its military on high alert after reports surfaced that signs have been detected of a possible missile launch by the North.
Seoul claims that the North had attempted four test launches of the missile back in April and May, all of which failed.
Tensions have been flaring in the region since January, when North Korea said it had successfully detonated a hydrogen bomb, its fourth nuclear test, and vowed to build up its nuclear program as deterrence against potential aggression from the US and its regional allies.
A month later, Pyongyang launched a long-range rocket which it said placed an earth observation satellite into orbit. However, Washington and Seoul denounced it as a cover for an intercontinental ballistic missile test.
Pyongyang was recently placed under the toughest UN sanctions in two decades. The country, however, has pledged not to relinquish its nuclear power unless the US ends its hostile policy and dissolves the US-led military command in South Korea.
All exploded in midair or crashed, according to South Korean defence officials.In April, North Korea attempted unsuccessfully to launch three suspected Musudan missiles.
South Korea says North Korea has fired another suspected mid-range missile, its second today.
No other details were immediately available.
Earlier, North Korea fired a suspected powerful new Musudan mid-range missile from its east coast, but the launch is believed to have failed, the South Korean military said.
A statement from South Korea's Joint Chiefs of Staff gave no further details on that launch from near the east coast city of Wonsan.
A US official also said the launch appeared to be another failure, adding that the US was assessing exactly what had happened.
Four earlier attempts to fire suspected Musudan missiles ended in failure in recent months.
The intermediate-range Musudan missile has raised concerns because its potential 3500km range puts US military bases in Asia and the Pacific within its striking range.
All exploded in midair or crashed, according to South Korean defence officials.In April, North Korea attempted unsuccessfully to launch three suspected Musudan missiles.
Earlier this month, North Korea had another missile launch failure.
South Korean officials didn't identify the type of missile launched on June 1, but South Korea's Yonhap news agency said it was also a Musudan.
Before April's suspected launches, North Korea had never flight-tested a Musudan missile, although one was displayed during a military parade in 2010 in Pyongyang, its capital.
The launches appear linked to North Korean leader Kim Jong Un's order in March for nuclear and ballistic missile tests.
The order was an apparent response to US-South Korean military drills, which North Korea views as an invasion rehearsal.
Despite the repeated failures, the launch attempts show the North is pushing hard to upgrade its missile capability in defiance of US-led international pressure.
The North was slapped with the strongest UN sanctions in two decades after it conducted a fourth nuclear test and a long-range rocket launch earlier this year.
Earlier, at a Washington briefing, Pentagon spokesman Peter Cook said that if North Korea were to conduct another missile test, it "would be another violation of UN resolutions".
"It would be another provocative action. So we certainly would urge North Korea to refrain from doing that sort of thing," Cook said.
North Korea has recently claimed a series of key breakthroughs in its push to build a long-range nuclear missile that can strike the American mainland.
But South Korean officials said the North doesn't yet possess such a weapon.
The North has already deployed a variety of missiles that can reach most targets in South Korea and Japan, including American military bases in the two countries.
The Korean Peninsula remains in a technical state of war because the 1950-53 Korean War ended with an armistice, not a peace treaty.
About 28,500 US soldiers are stationed in South Korea to deter possible aggression from North Korea.