South Korea's military remains on high alert for a fifth Northern missile test
North Korea appears to have launched a ballistic missile from a submarine off its east coast, South Korean officials say.
The missile was fired to the northeast of the coastal town of Sinpo, but it was not immediately clear where it had landed.
South Korea's Yonhap news agency said it flew "for a few minutes".
North Korea has recently launched a number of missiles and artillery shells into the sea in an apparent response to joint US-South Korea military drills and sanctions over a nuclear test and a rocket launch carried out by Pyongyang.
It is widely believed to have been developing a submarine-based missile system for some time and attempted to fire such a missile last year.
However, tests were largely thought to have been a failure and footage appears to have been edited to suggest success, according to experts.
Analysts point out that the latest belligerence comes before next month's ruling party congress, which could further cement Kim Jong-Un's hold on power.
There are also concerns that Pyongyang is planning a fifth nuclear test, with South Korea's military on high alert for one to be carried out "at any time".
Satellite images suggest tunnel excavation may have resumed at the the Punggye-ri site, where the country's last three nuclear tests took place.
"Pyongyang has clearly demonstrated, with its fourth nuclear detonation this past January, the ability to conduct detonations on short notice while masking indicators of its preparations from satellite view," a report by the 38 North website, run by the Johns Hopkins University's School of Advanced International Studies, said.