South Korean troops shot dead a man trying to swim across a border river into North Korea on Monday after he ignored repeated warnings to turn back, the defence ministry said.

A ministry spokesman said he was carrying a South Korean passport that identified him as Nam Yong-Ho, 47.

Fatal shore: The Imjin River, where the South Korean national was shot by his own nation's troops. Credit:LEE JAE-WON

According to the spokesman, Mr Nam had approached the bank of the Imjin river that makes up part of the western border with North Korea.

He was spotted by soldiers manning a nearby guard post, who fired warning shots and shouted at him to turn back.