North Korea test-fired Sunday a ballistic missile, the latest in a series of launches which have sparked international condemnation and threats of tougher UN sanctions.
The South's military said it could not yet identify the type of missile fired from Pukchang in South Pyongan province but it travelled about 500 km (311 miles).
Washington described it as a medium-range missile.
"Our military is closely monitoring signs for additional provocation by the North Korean military and we are keeping a full military readiness," said a statement from the South's Joint Chiefs of Staff.
Source: AFP