HONG KONG — China revealed on Sunday that North Korea seized a Chinese fishing boat this month and detained its crewmen, who remain in custody, an episode likely to worsen recent discord between the two.

The vessel’s owner, Yu Xuejun, called the Chinese Embassy in Pyongyang, the North Korean capital, on May 10 to seek help, the Chinese Ministry of Foreign Affairs said in a brief statement issued through Sina Weibo, the country’s Twitter-like microblog service. Mr. Yu was not on the boat when it was seized.

“The embassy immediately made representations to the consular affairs bureau of the North Korean Ministry of Foreign Affairs, asking that North Korea release the vessel and the crew as soon as possible, and ensure the safety of the lives and property of the detained crew, as well as their legitimate rights,” the Chinese ministry statement said.

The statement did not explain why the ministry waited so long to reveal the seizure, which came during a time of tensions with North Korea, a country that depends on Beijing for diplomatic and economic support.