Pyongyang fired two unidentified projectiles on Monday, according to the South Korean Defence Ministry.
"The military is monitoring for additional launches and maintaining readiness," the South's Joint Chiefs of Staff added.
The two devices are said to have been fired eastwards over the sea from the Wonsan area on the east coast.
The development comes amid reports that DPRK leader Kim Jong Un attended military excercises on Friday.
North Korea carried out a series of weapons tests in late 2019: the last time was in November when Pyongyang launched two short-range projectiles into the Sea of Japan.