Beijing called on Pyongyang to release a Chinese fishing boat and its crew seized earlier this month by unidentified North Korean men.

The Chinese Embassy in Pyongyang says it has sought the release of the 16 crew members and the vessel which was “grabbed” by armed North Korean men in Chinese waters on May 5. A ransom of 600,000 yuan ($100,000) was being demanded by the kidnappers, according to Yu Xuejun, the owner of the boat.

“The Chinese embassy promptly made representations to the… North Korean Foreign Ministry, asking the DPRK side to release the boat and the fishermen as soon as possible,” Counsellor Jiang Yaxian of Beijing’s embassy in Pyongyang was quoted by the Xinhua news agency as saying.

Jiang said the embassy would “continue efforts to ensure that the issue will be properly addressed at an early date”.

Chinese Foreign Ministry spokesman Hong Lei urged North Korea to “effectively safeguard the legitimate rights and interests” of the Chinese fishermen.

The incident comes as the latest sign of discord between the two close allies following the North’s third nuclear test in February. Beijing backed expanded international sanctions on Pyongyang over the test, including a suspension of financial transactions with North Korea’s main foreign exchange bank.