South Korean officials said earlier that South Korea and Japan were jointly investigating whether the fishing boat had violated Japanese waters near disputed islands roughly equidistant from both countries.

Last year, Japan arrested a Chinese fishing trawler captain after his boat collided with Japanese patrol vessels near isles disputed between Tokyo and Beijing. Ties between the two countries chilled after the incident.

Tokyo’s assertions of its sovereignty over the isles that Seoul also claims, known as Dokdo in South Korea and Takeshima in Japan , have in the past sparked protests in South Korea, where bitter memories linger of Japan’s 1910-1945 colonization of the peninsula.

“We are still doing an investigation and have to wait until its result comes out. The boat crew claimed that due to an operational malfunction, the boat had drifted,” a Korea Coast Guard spokesman said.

South Korea’s Yonhap news agency said the patrol boats had been involved in a standoff, but both Japanese and South Korean officials played down the report.

Yonhap said the incident involving a 29- ton fishing boat had taken place in waters about 70 km (45 miles) southwest of the disputed islands.