Koreas resume artillery exchange

North Korea resumed firing artillery Thursday near its disputed western sea border with South Korea, an official said, a day after the country fired dozens of shells and prompted South Korea to fire back a barrage of warning shots.

North Korea fired several rounds of artillery toward the border early Thursday and the shells are believed to have landed in North Korean waters, said an official at the Joint Chiefs of Staff said, speaking on condition of anonymity.

On Wednesday, South Korean officials said the North fired about 30 rounds of artillery from its coast and the South immediately responded by firing 100 warning shots from a marine base on an island near the disputed sea border.

On Tuesday, North Korea's designation of no-sail zones fuelled speculation the North may be preparing to conduct another round of missile tests.

The no-sail zones were designated south of the western maritime border in South Korean-held waters from Jan. 25 to March 29, South Korean Defence Ministry officials told The Associated Press and Yonhap on Tuesday.

North Korea has made no-sail announcements prior to carrying out previous missile tests and military manoeuvres but has also issued the sailing restrictions in anticipation of extended periods of bad weather.

The two countries, technically still at war since their 1950-53 conflict ended with an armistice, have clashed in the past in waters claimed by both sides.

The most recent incident was a brief gun battle in November that left one North Korean sailor dead and three others wounded, according to Yonhap news agency. The dispute over where to draw the maritime boundary also led to naval skirmishes in 1999 and 2002.

Nuclear negotiations have stalled

South Korea accused the North of launching ballistic missiles last summer off its eastern coast, in violation of a UN resolution prohibiting Pyongyang from testing all but certain short-range cruise missiles.

Ballistic missiles are guided during their ascent out of the atmosphere and fall freely when they descend, in contrast with shorter-range cruise missiles that fly low and straight to their target.

The ban on medium and longer-range missiles came after it was revealed North Korea had conducted an underground nuclear test last May.

The naval tensions between the two countries come as the two countries continue complicated diplomatic negotiations over the North's nuclear weapons program. In recent weeks North Korea has alternated between overtures of friendship and warnings of retaliation with its southern neighbour.

Multilateral talks between the North and regional powers — including the U.S., China and Japan — have also stalled because of the North's insistence of one-on-one talks with the United States to formally end the Korean War.

The U.S. has said it would meet with North Korea, but only after the multilateral talks take place.