A man has been shot dead while trying to swim to North Korea from the South, according to reports.
The man jumped into the Imjin river and ignored warnings to stop, the BBC said.
Defections from the North to the South are common, according to ITV, but people rarely try to go the other way.
According to the AFP news agency, soldiers shouted at the man to turn back, and fired warning shots.
"The soldiers opened fire and his body has been retrieved," a South Korean official said.
The shooting came after the demilitarised Kaesong industrial complex in North Korea was reopened for business, five months after work stopped as tensions between the warring neighbours escalated.
South Korean business chiefs welcomed the restarting of work, but said they had made heavy losses as a result of the enforced closure.
More than 50,000 North Koreans work in 123 South Korean factories in the zone.
The restart is being described as a trial, the BBC reported.