Image copyright AP Image caption The demilitarised zone is one of the most heavily fortified borders in the world

North and South Korea briefly exchanged gunfire over their heavily fortified land border, South Korea says.

North Korean troops approached the demarcation line separating the two sides, prompting South Korean soldiers to fire warning shots, officials said.

The North Koreans returned fire, and the sides exchanged shots for about 10 minutes, they added. There were no reports of injuries.

There were similar border skirmishes earlier this month.

It is not clear if the increasingly frequent clashes are the actions of local soldiers in a tense situation, or part of a wider provocation by either side, the BBC's Stephen Evans in Seoul says.

Last week, military officers from the two sides met at a border village to try to ease tensions, but no agreement was reached.

On 10 October, North Korean troops fired at balloons being released across the border from South Korea, prompting the South to return fire.

Image copyright Reuters Image caption Activists released balloons carrying leaflets denouncing the North Korean government on 10 October

Activists in South Korea frequently float balloons carrying leaflets condemning North Korean leader Kim Jong-un over the border - a move that angers the North.

Earlier in October, North and South Korean ships exchanged warning shots after a North Korean patrol boat crossed a disputed maritime border, South Korea said.

The two Koreas are separated by the heavily fortified Demilitarised Zone.

They have technically been at war since the 1950-53 Korean War ended in an armistice rather than a peace treaty.