SEOUL (AFP) - China's president arrived in Seoul Thursday for a state visit seen as a snub to Beijing's traditional ally North Korea, whose nuclear weapons ambitions will dominate talks with South Korean leader Park Geun Hye.
It was Xi Jinping's first trip as head of state to the perennially volatile Korean peninsula, and will mark his second summit with Park, who visited China last year.
North Korean leader Kim Jong Un is still waiting for an invitation to Beijing - a calculated rebuff that speaks 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 Leeds University.
In what some saw as a display of pique at Xi's visit, North Korea conducted a series of rocket and missile launches over the past week and pledged further tests in the future.
And 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.
After Xi and Park hold their summit, the two leaders are expected to sign a joint communique, with Seoul hoping for a strong statement on North Korea's nuclear weapons programme.
But analysts said Beijing was unlikely to up the rhetorical ante by any significant degree.
"That would go against China's traditional diplomatic pattern," said Kim Joon Hyung, professor of politics at Handong Global University.
"Xi will probably keep to the general line of urging the denuclearisation of the Korean peninsula, rather than criticising the North directly," Kim added.
As the North's diplomatic protector and chief economic benefactor, China has repeatedly 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 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.
The wider background to 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$343 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," 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.
"But South Korean presidents change every five years. If liberals return to power in 2018, the left's neutralist and Yankee-bashing tendencies might come to the fore," he said.
The military ambitions of the other main US ally in the region, Japan, is also likely to figure in Thursday's summit talks, with both China and South Korea concerned by the recent change to its pacifist constitution.