Artillery fire on Korean border

North Korea has fired artillery shells across its western maritime border, prompting return fire from South Korea, BBC News reports, citing local officials.

Dozens of the shells landed on a South Korean island, from which plumes of smoke are rising. At least four soldiers are said to have been hurt.

"A North Korean artillery unit staged an illegal firing provocation at 1434 PM (0534 GMT) and South Korean troops fired back immediately in self-defence," a South Korean defence ministry spokesman told AFP.

South Korea has issued its highest non-wartime alert in response.

This is said to be one of the most serious incidents between the two since the Korean War in the 1950s, according to BBC News.

Top leaders are meeting in an underground bunker in Seoul over the incident, Reuters news agency reported.

The incident comes days after North Korea revealed it had a modern uranium enrichment plant - potentially giving it a second route to a nuclear weapon.

Earlier, the US ruled out more denuclearisation talks while Pyongyang continued to work on the facility.

This western maritime border has been the scene of numerous clashes between the two Koreas in the past.

In March, a South Korean warship went down near the border with the loss of 46 lives.

International investigators say a North Korean torpedo sank the ship, although Pyongyang denies any role in the incident.

Since then relations between the two neighbours - who have not signed a peace treaty since the 1950-53 Korean War - have been very tense.