A North Korean missile launch has failed, South Korean defence officials say, but it is unclear how many were fired or what exactly was being tested.
The US military said it detected a missile which appeared to explode within seconds of being launched.
North Korea is banned from any missile or nuclear tests by the United Nations.
However, it has conducted such tests with increasing frequency and experts say this could lead to advances in its missile technology.
Earlier this month, the North fired four missiles that flew about 1,000km (620 miles), landing in Japanese waters.
This test came from the eastern coastal town of Wonsan and will be seen as a response to annual military drills under way between the US and South Korea, which the North sees as preparation for an attack on it.
North Korea is believed to be developing an intercontinental ballistic missile that could strike the US, and has previously claimed it had successfully miniaturised nuclear warheads so they can fit on missiles.
However, most experts believe the North is still some time away from being able to realise such a goal.
Analysis: Stephen Evans, BBC News, Seoul
Today's failure indicates that North Korea's space programme still has some way to go before its blood-curdling threats to turn Seoul and Washington into seas of flame are achievable.
Some experts also believe that the salvo of four missiles fired towards Japan two weeks ago may actually have been five, with one launch failing.
In addition to its missile failures, North Korea is not thought to have developed heat-resistant material necessary to launch a truly long-range intercontinental ballistic missile. But progress does seem to be being made.
Last weekend, North Korea conducted a rocket engine test that its leader Kim Jong-un claimed was a breakthrough in its rocket technology. This has not been confirmed by independent experts.
It came as US Secretary of State Rex Tillerson visited Japan, South Korea and China for talks on North Korea's recent actions, including its two most recent nuclear tests.
Mr Tillerson had said a military option was on the table if the North threatened the South or US forces.