North Korea fired 100 artillery shells into the sea Monday in a live-fire drill near the eastern maritime border with South Korea that followed a recent series of missile tests.

North Korea fired 100 artillery shells into the sea Monday in a live-fire drill near the eastern maritime border with South Korea that followed a recent series of missile tests.

The drill began shortly before midday (0300 GMT) using land artillery units based at the eastern tip of the Demilitarized Zone that bisects the Korean peninsula, the South's Joint Chiefs of Staff (JCS) said.

It lasted for 30 minutes and about 100 shells, some with a range of around 50 kilometers (30 miles), fell into waters north of the eastern sea boundary, a JCS spokesman said.

None of the shells crossed into South Korean waters.

South Korean border troops were already on heightened alert after a series of short-range ballistic missile tests by the North in recent weeks, including the firing of two Scud missiles into the Sea of Japan (East Sea) on Sunday.

"Today's exercise was seen as a show of force towards our side," a South Korean defence ministry spokesman told AFP.

North Korea often conducts tests and drills as a show of displeasure, and Sunday's missiles were fired after it denounced an upcoming South Korean-US naval exercise.

The annual drill, from July 16-21, involves the US aircraft carrier George Washington, which arrived in the southern port of Busan on Friday.