A South Korean fishing boat missing in the Sea of Japan has been detained by the North, coastguard officials say.
The officials said the crew of the Daeseung was being investigated by North Korean authorities.
Tension remains high between the Koreas amid a naval exercise carried out by the South in the Yellow Sea.
The exercises were a show of force after the North was blamed for sinking a Southern warship in March.
Authorities in the boat's home South Korean port of Pohang said the Daeseung had stopped sending signals after a fishing trip in the Sea of Japan, known in Korea as the East Sea, on Saturday.
The South Korean coastguard said in a statement: "We have found out that our fishing vessel is being investigated by North Korean officials in the presumed North Korea exclusive economic waters in the northern East Sea.
"The South Korean government, according to international law, wants the swift resolution to the matter and the safe return of its vessel and its fisherman."
The vessel has four South Koreans and three Chinese on board.
Media reports in the South say the Daeseung is being towed to the Northern port of Songjin.
North Korean media has so far made no comment on the latest reports.
There have been frequent incidents in recent years involving fishing boats of both sides in the disputed waters.
The North, which denied any involvement in the sinking of the Cheonan warship in March with the loss of 46 sailors, had pledged "strong physical retaliation" for the five-day naval exercises.
The South also recently carried out massive naval exercises with US forces in the Sea of Japan.
The latest exercises, in the Yellow Sea, are the South's biggest-ever anti-submarine drills, with some 4,500 personnel taking part near the disputed maritime border.
The South said that although its ships would stay clear of the disputed boundary, marines stationed on islands close to the border would conduct live-fire exercises.
In North Korea's official media, a statement attributed to military leaders called the exercises a "direct military invasion aimed at infringing upon the DPRK's [North Korea's] right to self-defence".