South Korea’s military has returned a North Korean boat and its seven crew members across the countries’ disputed western sea boundary a day after they drifted into waters near a border island.

South Korea’s navy fired warning shots on Tuesday to chase away a North Korean patrol vessel that temporarily crossed the so-called Northern Limit Line while pursuing the boat near Baekryeong island.

The seven crew members told South Korean military officials they drifted south of the boundary because of navigation mistakes and mechanical problems, and expressed a desire to return to North Korea, Seoul’s Defence Ministry said.

South Korea’s navy has often fired warning shots to repel North Korean vessels crossing the countries’ poorly marked sea border, but there also have been some deadly clashes over the years.

South Korea blamed North Korea for an attack on one of its warships in 2010 in which 46 sailors were killed, but the North denied responsibility.

South Korea has patrolled waters around the Northern Limit Line for decades after it was drawn up by the UN command at the end of the 1950-53 Korean War.

North Korea does not recognise the line and insists upon a boundary that encroaches deeply into waters currently controlled by the South.