North Korea has test-fired a ballistic missile from a submarine, South Korea's military says.
It says the missile was launched in waters east of the Korean peninsula - the latest in a recent series of tests.
North Korea, which is developing nuclear weapons, is banned by UN resolutions from any use of ballistic missile technology.
The US and South Korea on Friday agreed to deploy a missile defence system to counter threats from Pyongyang.
The South Korean military says the missile was launched at about 11:30 local time (02:30 GMT) off North Korea's port of Sinpo.
It did not provide further details.
Pyongyang has so far made no public comments on the issue.
On Friday, Seoul and Washington agreed to deploy the Terminal High Altitude Area Defense (THAAD) anti-missile system in the wake of intensifying threats from the North.
It is unclear exactly where it will be sited and who will have final control.
Earlier this week, the US imposed sanctions on North Korean leader Kim Jong-un - a move Pyongyang described as an "open declaration of war".
This was the first time sanctions have been used against Mr Kim by the US, as it declared him directly responsible for human rights abuses in his country.
Pyongyang has reportedly warned that it will close down all diplomatic channels with the US unless the blacklisting is revoked.
In January, North Korea conducted its fourth nuclear test, claiming it to be its first using a hydrogen bomb. Shortly after that Pyongyang launched a satellite, widely seen as a test of long-range missile technology.