SEOUL (AFP) - China and South Korea issued a joint call for the denuclearisation of the Korean peninsula at a summit in Seoul Thursday that was seen as a pointed snub of nuclear-armed North Korea by Beijing.

In a joint statement after their talks, the Chinese and South Korean presidents, Xi Jinping and Park Geun-Hye, reaffirmed their "firm opposition" to the development of nuclear weapons, but seemed divided on how to best persuade the North to give up its bombs.

While Ms Park told reporters that the two sides had agreed to use "all means" possible to bring denuclearisation about, Mr Xi stressed that "dialogue and negotiation" were the best way forward.

The joint statement marked no departure from established Chinese and South Korean policy towards North Korea, but the fact that it was released at a summit in Seoul carried significant symbolic weight.

It was Mr Xi's first trip as head of state to the perennially volatile Korean peninsula, and his second summit with Park, who visited China last year.

North Korean leader Kim Jong-Un is still waiting for an invitation to Beijing and Mr Xi's decision to visit Seoul before Pyongyang was seen as a calculated rebuff that spoke to the strained relationship between Pyongyang and its historic and most important ally.

"No previous Chinese leader has put South Korea before and above the North like this," said Aidan Foster-Carter, a Korea expert at Britain's Leeds University.

In what some saw as a display of pique at Mr Xi's visit, North Korea had conducted a series of rocket and missile launches over the past week and pledged further tests in the future.

Seoul had been hoping that Thursday's joint statement would include a strongly-worded warning to Pyongyang, but analysts had forecast that Beijing was unlikely to up the rhetorical ante by any significant degree.

It made no mention of North Korea's nuclear tests, although in her comments afterwards Ms Park said both sides had reaffirmed their "resolute opposition" to any further detonations.

The statement did stress the importance of finding a way to get the long-stalled six-party talks on North Korea up and running again.

Beijing has repeatedly pushed for a resumption of the six-party process - involving the two Koreas, China, the United States, Japan and Russia.

But Seoul and Washington insist that Pyongyang must first make a tangible commitment to abandoning its nuclear weapons programme.

As the North's diplomatic protector and chief economic benefactor, China has been pressured by the international community to use its leverage to rein in Pyongyang's nuclear ambitions.

But while Beijing has become increasingly frustrated with the North's missile and nuclear tests, it remains wary of penalising the isolated state too heavily.

It is especially anxious to avoid any regime collapse that would result in a unified Korea with a US troop presence on its border.

Washington has played up Mr Xi's two-day visit as evidence of Pyongyang's deepening diplomatic isolation.

"The symbolism of a visit by a Chinese leader to Seoul against the backdrop of tensions between North Korea and its neighbours... is pretty striking," US Assistant Secretary of State Daniel Russel told AFP.

But Pyongyang scored a diplomatic victory of its own Thursday, as Japan announced it was revoking some of its unilateral sanctions on North Korea after progress in talks on the Cold War kidnapping of Japanese nationals.

Japan and North Korea do not have formal diplomatic ties, and the announcement by Prime Minister Shinzo Abe is a significant step forward for a relationship that has been testy for decades.

The wider background to Mr Xi's trip includes China's response to the US "pivot to Asia" and the battle between the two major powers for regional influence.

China is currently South Korea's largest export market and two-way trade stood at around US$275 billion (S$ 342 billion) last year, but analysts say Beijing wants to move beyond economic ties and promote political and security links.

This leaves Seoul with a difficult balancing act, given its historic military alliance with the United States.

There are currently around 29,000 US troops stationed in South Korea, which is also protected by the US nuclear umbrella.

So how far would South Korea be willing to go in developing its ties with China beyond the economic sphere?

"Partly it depends who holds power in Seoul," Mr Foster-Carter wrote on the NK News website. "Conservatives like Park will ensure the US alliance is not weakened, especially while North Korea continues to snarl."