North Korean officials have demanded payment before they release Chinese fishing boats with a total of 29 men onboard, Chinese media reported on Thursday, in a rare public spat between the neighbors and longtime allies.The Chinese owners of the boats said they were seized by a North Korean gunboat on May 8 in the Yellow Sea, between China and North Korea, the Beijing News reported.The owners said the vessels were fishing in Chinese waters. North Korea has not made any public comment on the case.The North Koreans holding the boats and sailors demanded payment of 1.2 million yuan ($189,800) for releasing them, then cut their price to 900,000 yuan and set a deadline of Thursday, Zhang Dechang, owner of one of the captured boats told the newspaper, which called the demand a "ransom”.The 29 sailors who were on board the boats are now in North Korea, said one captured seaman in a call with an owner, the newspaper added.China is the key economic and diplomatic backer of North Korea, seeing it as a buffer against U.S. influence in the region. Beijing is a major supplier of food aid and oil to the North, which remains isolated by sanctions over its nuclear ambitions and rocket launches.China has been quietly pressing North Korea to scrap plans for a third nuclear test, sources with knowledge of closed-door talks between the countries have told Reuters.Pyongyang has sought to shore up ties with Beijing through frequent visits and praise of their friendship, but the North can also be resentful about what it sees as infringements of its territory, and Chinese dominance of relations.It was unclear whether the seizure of the boats was authorized by the North Korean government, or was the initiative of local officials.The Chinese Foreign Ministry told the Beijing News that the incident was a "fisheries case”, and will be resolved as soon as possible. The Chinese Foreign Ministry did not immediately answer phone calls and faxes.