A top official and confidante of North Korean leader Kim Jong-Un Wednesday met a senior Chinese official in Beijing, at a time of strained relations and ahead of a China-US summit.

Choe Ryong-Hae, director of the Korean People's Army politburo, flew to Beijing with a handful of senior military and ruling party officials, the Korean Central News Agency said, highlighting his role "as a special envoy" of the North's young leader.

Choe met Wang Jiarui, head of the ruling Chinese Communist Party's International Department, the official news agency Xinhua said, without giving further details.

Choe is believed to be the highest ranking North Korean party official to visit China -- Pyongyang's sole major ally and chief economic benefactor -- since late leader Kim Jong-Il in August 2011.

Kim Jong-Un has never visited since he took over after his father's death in December 2011. He sent his uncle Jang Song-Thaek, one of the powerful figures in Kim's inner circle, to Beijing in August last year.

The trip comes at a sensitive time for a relationship which has been sorely tested in recent months by Pyongyang's refusal to heed Beijing's warnings against provoking the international community with its nuclear programme.

China has long been the North's chief diplomatic protector. But it sided with the rest of UN Security Council in imposing sanctions after the North's long-range rocket test in December last year, and its nuclear test in February.

The sanctions triggered a dangerous cycle of escalating military tensions on the Korean peninsula, during which China came under enormous US-led pressure to rein in its wayward ally which was threatening nuclear strikes against the US and South Korea.

Professor Yang Moo-Jin of Seoul's University of North Korean Studies said the timing of Choe's visit was significant ahead of a scheduled June 7-8 summit between US President Barack Obama and China's new leader Xi Jinping.

And South Korea's new president, Park Geun-Hye, is expected to hold a summit with Xi in Beijing in late June.

"Choe is Kim Jong-Un's closest confidante, so Kim is sending his highest possible envoy to China ahead of the US summit," Yang told AFP.

"This will be Kim's way to deliver his message to Obama concerning peace on the Korean peninsula and the nuclear issue," he added.

Seoul and Washington have held out the prospect of talks with North Korea, but only if it displays a firm commitment to abandoning its nuclear weapons programme.

The North has made it clear that its nuclear deterrent is not up for negotiation, but observers said Choe might be empowered to offer some assurances or concessions to China.

"He's Kim's top military guy, so clearly the North's nuclear and missile programme will be on the agenda," said Cheong Seong-Chang, an analyst at the Sejong Institute think-tank in Seoul.

"China is looking for some sign of compromise, and Choe might offer an assurance not to conduct any more nuclear tests for now," Cheong said, adding that the North might seek a Kim summit with Xi in exchange.

The bilateral relationship, forged in the 1950-53 Korean War, has weakened significantly over the years, as China's economic transformation has distanced it from the ideological rigidity of the dynastic Kim regime across the border.

In line with UN sanctions, Beijing has moved to restrict Pyongyang's financial operations in China which the international community says are the major conduit for funding its nuclear weapons programme.

The strain in relations was reflected most recently when a Chinese fishing boat with 16 crew was seized by unidentified North Koreans.

The detention caused outrage online in China, with Internet users calling on Beijing to take a tough stance against Pyongyang.

Cho Han-Bum, an analyst at South korea's Korea Institute for National Unification, said Choe's trip would almost certainly include talks on a possible China visit by Kim.

"The North's threats and military brinkmanship during the recent crisis didn't reap much in the way of reward, so Kim needs a boost and a China visit would help cement his legitimacy as leader," Cho said.