between the two countries. North Korean state media called the shots a "deliberate provocation" and Pyongyang has accused Seoul of risking "uncontrollable" tensions.

The incident was made public as new South Korean President Lee Jae Myung departed Seoul on Saturday for a visit to Tokyo and Washington. Pyongyang has upped the ante in recent weeks, with leader Kim Jong Un's sister rebuffing efforts towards reconciliation made by Lee's government. The incident took place amid continuing work by North Korea since last year to permanently seal its border with the South.

A strip of no-man's land called the Demilitarised Zone (DMZ) separates the north and south, with intrusions often increasing tensions. The DMZ border is not fenced and the signposts are obscured by dense vegetation. South Korea's Joint Chiefs of Staff (JCS) said in a statement that some North Korean troops working in the border region crossed the military demarcation line between the two countries at about 15:00 local time in Seoul on Tuesday (07:00 BST). The soldiers later moved back to the north of the line, the JCS added.

North Korean Army Lt Gen Ko Jong Chol said Seoul's military used a machine gun to fire more than 10 warning shots towards its soldiers, according to state media.

"This is a very serious prelude that would inevitably drive the situation in the southern border area where a huge number of forces are stationed in confrontation with each other to the uncontrollable phase," state media said he added. Pyongyang has been dismissive of Seoul despite the June election victory of Lee, who had campaigned on improving inter-Korean ties. South Korea's military said later that month that it had suspended its loudspeaker propaganda broadcasts across the border to North Korea, as part of a bid to "restore trust" between the two sides. Pyongyang considers the loudspeaker propaganda broadcasts an act of war and has threatened to blow them up in the past. (BBC)