China's leadership is hitting a rough patch with ally North Korea under its new leader Kim Jong Un, as Beijing finds itself wrong-footed in episodes including Pyongyang's rocket launch and the murky detention of Chinese fishing boats.

The testy state of China-North Korea affairs became public this week after Chinese media flashed images of the fishing crews, some of the 28 crew members stripped to their longjohns, returning home after 13 days in North Korean custody accused of illegal fishing. The reports quoted the fishermen as saying they were beaten and starved, and the coverage unleashed furious criticism in China's blogosphere.

"The North Koreans are like bandits and robbers," China's Southern Metropolis Weekly newspaper quoted one fisherman as saying Tuesday. The story, shared thousands of times on China's Sina Weibo social media website, said the hijackers ripped down the Chinese flag on one boat and used it "like a rag."

While much remains unclear about the event — including whether the fishing boats were poaching in North Korean waters — to some Chinese observers it seemed like a slap on the face from Kim Jong Un, who took power after his father died in December.

"The context of what is happening now between China and North Korea is this: Since Kim Jong Il died, the Kim Jong Un regime has been unfriendly to China," said Shi Yinhong, an international relations expert at Renmin University in Beijing.

But even to the skeptics, the recent discord is unlikely to rupture an alliance that the countries' communist leaders like to say was "sealed in blood" in the Korean War. "They can weather it," said John Delury of Yonsei University's Graduate School of International Studies in South Korea.

Pyongyang remains heavily reliant on Beijing for diplomatic protection in the United Nations and for much of the country's food, trade and oil. Chinese leaders worry that without the Kims in power, a North Korean meltdown would send a destabilizing wave of refugees into China and give U.S. troops stationed in South Korea an opportunity to move closer to the Chinese border.

But in part because of its steadfast support, Beijing finds the lack of regard from Pyongyang all the more irritating. Relations between the sides are "very strained at the moment," said Stephanie Kleine-Ahlbrandt, a Beijing-based analyst with the International Crisis Group think tank.

The strains come as Beijing would like to coax the young Kim into launching bolder economic reforms to lessen North Korea's reliance on hand-outs and into easing regional tensions so as not to drive the U.S., South Korea and Japan into closer alliance.

The fishing fleet episode comes amid other diplomatic frictions.

Shi, the Chinese analyst, said Pyongyang failed to give Beijing a heads-up about a deal concluded with Washington in February for American food aid in return for concessions on North Korean missile and nuclear programs.

Pyongyang compounded the affront by testing a rocket that stoked regional tensions and drew strenuous Chinese objections. China called in the North Korean ambassador to Beijing and urged Pyongyang publicly to desist, to no avail. Pyongyang did not give Beijing advance notification of the launch last month, said Shi and others.

"They did not inform China in advance. The Chinese government is indignant," Shi said.

The United States and other critics called the rocket launch a cover for a test of missile technology, and the U.N. Security Council — with China's backing — strongly condemned the launch. North Korea said the rocket, which broke into pieces over the Yellow Sea shortly after liftoff, was meant to send an observational satellite into orbit.

Beijing rarely rebukes Pyongyang in public. Both governments prefer to keep their dealings out of public view, making it always difficult to assess the tenor of ties. Still, the perceived slights from Pyongyang contrast with Beijing's full-bodied embrace of Kim Jong Un. Within hours of Kim Jong Il's death, Chinese President Hu Jintao and other top leaders expressed support for the younger Kim's succession, and they have invited him to visit China.

Analysts said that there has been a marked fall-off in high-level diplomatic visits to North Korea by Chinese officials, but that could be attributed to North Korea's mourning period for Kim and a preoccupation with internal transition politics.

"Communication channels have never been broken between the two sides," said Shi Yuanhua, Director of Center for Korean Studies of Fudan University in Shanghai.

Some among China's North Korea watchers have criticized Beijing's seemingly unconditional support for North Korea as part of the problem. With little at risk, their thinking goes, Pyongyang is encouraged to engage in high-stakes policies.

South Korean intelligence reports and satellite imagery have shown new tunnel-digging at a North Korean nuclear test site in possible preparation for testing a nuclear device, its third in six years. If Pyongyang goes ahead, the test is likely to leave Beijing feeling further ignored, but without other repurcussions.

"Although Beijing would probably prefer North Korea not to conduct another rocket or nuclear test, it would not really alter the fundamental strategic calculus from the Chinese government's perspective," said Delury.