A small boat carrying suspected defectors from North Korea has been detained after it crossed into the South's waters, Seoul's military said.
It was detected on South Korea's side of the Northern Limit Line, the maritime boundary of the two Koreas.
The Joint Chiefs of Staff said the four people on board were "presumed to have defected" from North Korea.
Defections have become increasingly difficult since North Korean leader Kim Jong Un took power in 2011.
Border controls were also tightened further since the Covid-19 pandemic in 2020.
South Korean authorities did not release further details about the four North Koreans on board the wooden boat.
In May, a group of nine North Koreans crossed the western sea boundary aboard a fishing boat and were rescued by the coast guard.
Would-be defectors are typically detained and questioned for up to a month, in order to ascertain their motives for leaving the North.
They are then sent on to Hanawon, a resettlement centre where they are prepared for life in South Korea.
Earlier this month, Seoul said that Beijing forcibly repatriated a "large number" of North Korean defectors. Human rights groups said as many as 600 North Koreans had been sent back, and that they face imprisonment, sexual violence or even death once back in the North.
China does not recognise North Korean defectors as refugees. It claims they are "economic migrants" and has a policy of sending them back, despite requests from foreign governments and human rights organisations to reconsider its stance.
