File Photo of South Korean soldiers (Associated Press)

South Korean troops fired warning shots at North Korean soldiers who intruded on the buffer zone marking their heavily armed border, Seoul said today, in the first such skirmish this year.The incident occurred on Saturday morning when 10 North Korean soldiers crossed the border of the demilitarised zone separating the two Koreas, which remain technically at war, the South's defence ministry said.But the brief intrusion near Cheorwon, northeast of Seoul, triggered no exchange of fire as North Korean soldiers retreated without firing back, it said.The demilitarised zone, or DMZ, despite its name, is one of the world's most heavily militarised frontiers, bristling with watchtowers and landmines.There have been a series of minor skirmishes, involving exchanges of fire, along the inter-Korean land and sea borders in recent years.But this is the first time in 2015 South Korean soldiers have fired warning shots at North Korean troops for intruding in the DMZ, a ministry official told AFP.Cross-border tensions have flared at regular intervals this year, with North Korea conducting a series of ballistic missile tests in anger at annual US-South Korean military exercises.