A policeman holds up his hand as he stands guard outside the North Korean embassy in central Beijing, on May 17, 2012. North Korean officials have demanded payment before they will release Chinese fishing boats with a total of 29 men onboard, Chinese media reported. (David Gray/Reuters)

Unidentified North Koreans are demanding a payment to release 29 Chinese fishermen whose boats were seized last week, Chinese media outlets reported Thursday, in a rare public dispute between the neighbors and allies.

According to the Beijing News, armed North Koreans hijacked three Chinese vessels sailing in the Yellow Sea, between North Korea and China, on May 8. They initially asked for a ransom of $190,000 but later reduced the amount to $142,000, the newspaper reported.

The fishing boats were seized in Chinese waters, China Central Television said.

North Korea offered no official comment on the incident, and there was no indication that the alleged gunmen were operating on orders from the Pyongyang government. Still, the incident threatened to strain ties between the isolated North and its chief ally, which are known to engage in behind-the-scenes bickering even as they issue public avowals of friendship.

China has been party to numerous quarrels in the Yellow Sea, but such incidents mostly involve South Korea, not the North. Chinese Foreign Ministry spokesman Hong Lei said Beijing has been in contact with officials in Pyongyang through “relevant channels.”

“We hope this problem will be appropriately solved as soon as possible,” Hong said.

According to China’s Global Times newspaper, the fishermen were being held in a small cabin with no food. Days earlier, the paper reported that the North Korean captors had agreed to release the fishermen but that the deal fell through because the ransom-seekers “failed to show up at an appointed location.”

The North Koreans, the same report said, were demanding payment by Thursday. But there was so sign Thursday of a resolution.

The captors “were wielding guns, so the fishermen didn’t dare resist,” Zhang Dechang, owner of one of the boats, told the Global Times. “We hope related departments can help us free the crew.”

With its nuclear tests and military provocations, Pyongyang has long been a source of frustration to Beijing, whose officials quietly complain about the authoritarian country that keeps the region on edge.

Still, in recent years, China has only tightened its bond with North Korea, having determined that the country’s stability is essential to Chinese security. As long as the country remains under the leadership of Kim Jong Eun, heir to the North’s autocratic dynasty, Beijing does not have to worry about a unified and democratized Korean Peninsula, presumably governed from Seoul and close to the United States.

China is North Korea’s dominant trading partner and chief supplier of aid, and Beijing has been reluctant to condemn the reclusive country for violating international resolutions.