South Korean soldiers fired warning shots after North Korean troops crossed the border by mistake, Seoul’s military said on Tuesday.

The incident at the Demilitarised Zone (DMZ) on Sunday comes as tensions continue to rise between the two Koreas.

A small group of North Korean soldiers carrying field tools including pickaxes entered South Korea at 12:30 local time (05:30 GMT), Seoul’s military said. They were among 20 who were in the border area at that time.

They retreated immediately after the South Koreans fired the warning shots.

In recent weeks, the North has flown hundreds of rubbish-filled balloons to border towns in the South.