China is urging North Korea to release a Chinese fishing boat whose owner says it was seized by gun-toting North Koreans earlier this month and held for ransom, in the latest irritant in relations between the neighboring allies.

Boat owner Yu Xuejun, who wasn't aboard, first publicized the seizure on his microblog late Saturday, and on Monday posted that his terrified captain had communicated to him a new deadline to pay a ransom.

"My captain gave me the phone. His voice was trembling. Could feel he was very afraid. Told me no later than 5 p.m. today," Yu wrote on a verified Tencent Weibo account. The tweet was accompanied by photos of the captain and 15 sailors.

Yu wrote over the weekend that North Koreans seized his boat May 5 in what he maintained were Chinese waters, and that they demanded a 600,000 yuan ($100,000) ransom. Yu was quoted by the Southern Metropolis on Sunday as saying the North Korean side had first asked for the ransom to be paid by noon Sunday to a company in Dandong, a city in northeastern China on the North Korean border, or that they would confiscate the boat and repatriate the crew.

Yu wrote Monday that he suspects his crew had been mistreated.

The seizure of the Liaoning-based boat adds to China's frustration with North Korea over its recent tests of nuclear and rocket technologies in defiance of international efforts to curb the country's nuclear ambitions.

In addition, the Chinese government is under intense pressure domestically to ensure the safety of citizens who venture abroad or out to sea to seek their livelihoods. Another abduction by North Koreans of Chinese fishermen about a year ago — along with allegations they were beaten — sparked furious criticism among Chinese online.

"Whatever you call North Korea — rogue state or whatever — these kind of cases just keep happening," a Liaoning Maritime and Fishery Administration official who identified himself only by his surname, Liu, said Monday. "We had such cases last year and the year before. There's very little we can do to prevent them."

Yu's post asking for help from Internet users and China's Foreign Ministry was reposted and commented on more than 13,000 times.

In a sign that he was trying to increase pressure on the government, he wrote on Monday afternoon: "We can only hope the country can defend our rights."

"My boat was captured by foreign forces in my country's own waters. Of course we hope the government will support us fishermen and protect our lives and property," Yu wrote in response to a posted question on what he wanted the government and military to do.

At a routine Chinese Foreign Ministry briefing in Beijing, spokesman Hong Lei declined to answer a question about who China believed was behind the boat seizure, but made clear it was looking for the North Korean government to deal with it.

"China already filed a representation to North Korea through relevant channels, urging North Korea to properly handle the case as soon as possible, and earnestly ensure the fishermen's legal rights and safety and their property," he said.

The official Xinhua News Agency, in its first report of the incident late Sunday, said Chinese diplomats in the North Korean capital had received a request for help from Yu as early as May 10, and that they had demanded at the time that North Korea release the boat.

In an interview with China's Global Times newspaper, Yu said the kidnappers expertly removed a pair of global positioning systems and confiscated all communication devices after boarding the boat. He also told the paper that he couldn't afford the ransom and was concerned that the 20 days' food supply onboard would run out soon.

In May of last year, a North Korean boat hijacked three Chinese boats with 29 fishermen on board, reportedly for a ransom of $190,000. Two weeks later, the fishermen were freed — some of them stripped of everything but their long johns — and were widely quoted in Chinese media on their return as saying they had been beaten and starved.

A report by the Washington, D.C.-based Center for Strategic and International Studies in November last year said that the seizure of Chinese fishing boats by North Koreans to extract a payoff was "not unprecedented." It said that what was exceptional in last year's case was the publicity, whipped up by the vessels' owners and families of the captured sailors who were dissatisfied by the inaction of local officials.

China is North Korea's economic lifeline, providing nearly all of its fuel and most of its trade. North Korea's economic dependence on China is rising, following a standoff with South Korea that effectively shut an industrial park that was a rare source of hard currency. Still, Beijing has had difficulty persuading its neighbor to abandon its nuclear program, and early this year began joining Western nations in moves to punish Pyongyang with economic sanctions.

Xinhua, citing Chinese Embassy official Jiang Yaxian, said the embassy had contacted the North Korean Foreign Ministry's Bureau of Consular Affairs, "asking (North Korea) to release the boat and the fishermen as soon as possible."

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

Liu, the fishery official, said he was not sure where the boat was at the time of the seizure.

"It is not clear. The owner of the boat says it was in Chinese waters," Liu said.