N. Korea fires artillery shells to send 'grave warning' to S. Korea

North Korea fired artillery shells off its east and west coasts late on Tuesday, South Korea's military said, after Seoul kicked off annual defence drills aimed at boosting its ability to respond to the North's nuclear and missile threats.

The North fired some 100 shells into the sea off its west coast around 10 p.m. (1300 GMT) and shot a further 150 rounds off its east coast, the South's Joint Chiefs of Staff said in a statement on Wednesday.

North Korea said later that the shots were designed to send a "grave warning" to South Korea in response to its firing of dozens of artillery shells on Tuesday between 9:55 a.m. and 5:22 p.m.

The Korean People's Army (KPA) General Staff said the South's "war drill against the north is going on in a frantic manner".

"In order to send a serious warning once again, it made sure that KPA units on the east and west fronts conducted a threatening, warning fire toward the east and west seas in the night of Oct. 18, as a powerful military countermeasure," it said in a statement released by state media KCNA.

"The enemies should immediately stop the reckless and inciting provocations escalating the military tension in the forefront area."

The Hoguk drills, due to end on Saturday, are the latest in a series of military exercises by South Korea in recent weeks, including joint activities with the United States and Japan.