North Korea conducted a missile test off its east coast on Friday morning, but the launch appears to have failed, say US and South Korean officials.
The rocket has not yet been identified but is suspected to have been a previously untested "Musudan" medium-range ballistic missile.
The launch coincided with the birthday of North Korea's founding leader, Kim Il-sung.
It also comes amid particularly high tension on the Korean peninsula.
South Korea's Yonhap national news agency quoted government sources as saying that the missile was a type of intermediate-range ballistic missile known as a Musudan, also called the BM-25.
North Korean forces were seen recently moving two such missiles.
The report said it would be the North's first Musudan test, and that it may have at least 50 more.
The Musudan is named after the village in North Korea's northeast where a launch pad is sited.
It has a range of about 3,000 km (1,800 miles), which extends to the US Army base on the Pacific island of Guam, but not as far as the mainland US.
The US said it had tracked the latest launch, but could also not confirm details,
"We call again on North Korea to refrain from actions and rhetoric that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments and obligations," a State Department official said.
China also criticised what it called "the latest in a string of sabre-rattling that, if unchecked, will lead the country to nowhere," according to the official Xinhua news agency.
The BBC's Stephen Evans in Seoul says that even though it failed, the test illustrates the determination of current leader Kim Jong-un to get the ability to strike the United States, but also the North's technological limitations.
The North has made a series of threats against the South and the US since the UN imposed some of its toughest ever sanctions on the country.
The move was a response to the North's fourth nuclear test in January and its launching of a satellite in February, both of which broke existing sanctions.
The North has also been angered by South Korea and the US conducting their largest ever joint military exercises, which wrap up next week.
In March, North Korea said it had developed nuclear warheads small enough to fit on ballistic missiles. However, experts cast doubt on the claims.
The birthday of North Korea's founder - Mr Kim's grandfather - is significant. Four years ago, the North tried to celebrate it with a similar missile launch, but that too failed.
North Korea's rocket launches
- February 2016: Launch of rocket reportedly carrying satellite
- May 2015: North Korea announces it has successfully tested a submarine-launched missile for the first time, but scepticism is then poured on the claim
- Dec 2012: North Korea launches three-stage rocket, says it successfully put a satellite into orbit; US defence officials confirm object in orbit
- Apr 2012: Three-stage rocket explodes just after take-off, falls into sea
- Apr 2009: Three-stage rocket launched; North Korea says it was a success, US says it failed and fell into the sea
- Jul 2006: North Korea test-fires a long-range Taepodong-2 missile; US said it failed shortly after take-off