S Korea fires shots after North's soldiers cross border

They had breached the Military Demarcation Line running through the middle of the demilitarised zone (DMZ), where they were working about 11am on Thursday, South Korea said.

It is at least the third such incident this month. South Korea's military fired warning shots on Tuesday after dozens of North Korean soldiers breached the demarcation line.

The incident came after Russian President Vladimir Putin visited Pyongyang for the first time in 24 years earlier this week.