Gunmen wearing North Korean military uniforms assaulted the captain of a Chinese fishing boat and stole the vessel's fuel, the boat's owner, who had been held for two weeks, said after being released.
The seizure on May 5 in what owner Yu Xuejun said were Chinese waters was the latest irritant in relations between North Korea and a Chinese government increasingly frustrated with its neighbour and ally following tests of its nuclear and rocket technologies in defiance of UN bans. One of China's North Korea watchers said rogue border guards were probably responsible, rather than the government in Pyongyang itself.
Yu said in an interview that the men released on Tuesday were allowed to move around the boat while they were held captive, but were locked in a room at night.
He said the captain suffered an arm injury when he was beaten, but he has since recovered, and that no other crew member was harmed. They now planned to stay out at sea for another 10 days.
"The North Koreans only left the crew with one sack of rice and one sack of flour. But this shouldn't be a problem as there are a lot of boats in that region now, all from Dalian ," he said, referring to the northeastern port where his boat is based. "With their help, the crews will do OK for the next 8 or 10 days."
Yu publicised the boat's capture over the weekend on his Tencent Weibo microblog as a ransom deadline neared. China then publicly demanded that North Korea release the men, though Chinese officials have not said whether they believe the armed captors were operating on their own or under North Korean government authority.
No ransom was paid, Chinese Foreign Ministry spokesman Hong Lei said at a news briefing on Tuesday.
"We demand North Korea investigate this case fully and furnish China with details, and take measures to stop such cases repeating themselves," Hong said.
Yu also said he hadn't paid any of the 600,000 yuan (HK$752,000) ransom.
"We were working in our country's waters - why should I pay them?" he said. He had earlier written online that he couldn't afford it.
He said the captors "looked like soldiers, and the captain said they had guns and used force to take over the boat".
Yu posted co-ordinates on his microblog indicating the seizure took place about 100 kilometres from the westernmost point of North Korea and about 190 kilometres from Dalian.
That area is outside both countries' territorial waters - defined as 12 nautical miles from their shores - but within their overlapping "exclusive economic zones", which give them rights to resources including fish.
Yu said their captors took fuel and food, but navigation and communication equipment initially taken was returned.