The weapons were launched from South Pyongan province in an easterly direction over the sea, Seoul's Joint Chiefs of Staff said in a statement, without specifying the type of device involved.

"We are maintaining readiness and monitoring in case of additional launches," they added.

It is the latest in a series of launches by the North but the first since October 2, when it fired a sea-launched missile in a provocative move -- a submarine-based missile capability would change the military balance.

The North then walked away from working-level nuclear talks with the US in Sweden, and has since repeatedly urged Washington to come forward with a new offer by the end of this year.

Pyongyang is under multiple sets of international sanctions over its banned nuclear weapon and ballistic missile programmes, which it says it needs to defend against a possible US invasion.