US Secretary of State John Kerry met top officials of North Korea's key ally and aid provider China on Saturday to press them to rein in a defiant Pyongyang, seeking Beijing's help to defuse soaring nuclear tensions.
Kerry met first with China's foreign minister Wang Yi after flying in from talks in South Korea with President Park Geun-Hye, where he offered public US support for her plans to initiate some trust-building with the North.
The Korean peninsula has been engulfed by escalating military tensions and dire threats of nuclear war ever since North Korea conducted a rocket test last December and a nuclear test in February.
"Obviously there are enormously challenging issues in front of us, and I look forward to having that conversation with you today," Kerry told Wang.
Wang agreed the visit came at a "critical moment".
China has backed North Korea since the 1950-53 Korean War and could wield tremendous leverage over the isolated communist regime thanks to the vital aid it provides, including almost all of its neighbour's energy imports.
But analysts say it is wary of pushing too hard for fear of destabilising North Korea, which could send a wave of hungry refugees flooding into China and ultimately lead to a reunified Korea allied with the United States.
China and the US have a sometimes strained relationship, with Beijing uneasy over Washington's 'rebalancing' towards Asia, and Kerry's first visit to the region since becoming America's top diplomat has been completely overshadowed by the Korean crisis.
Washington is seeking to persuade Beijing to help rein in the bellicose threats from North Korean leader Kim Jong-Un, and bring Pyongyang back to the negotiating table over its suspect nuclear programme.
"I think it's clear to everybody in the world that no country in the world has as close a relationship or as significant an impact on the DPRK (North Korea) than China," Kerry said in Seoul after meeting South Korean leaders.
China is estimated to provide as much as 90 percent of its neighbour's energy imports, 80 percent of its consumer goods and 45 percent of its food, according to the US-based Council on Foreign Relations.
Despite intelligence reports that the North has prepared what would be a highly-provocative, medium-range missile launch, Park has in recent days made some conciliatory gestures to the regime in Pyongyang.
In a meeting with her ruling party officials on Friday, Park said the South should meet with the North and "listen to what North Korea thinks".
While Kerry berated Pyongyang's "unacceptable" rhetoric and warned that any missile launch would be a "huge mistake," he also took pains to stress US backing for Park's initiative.
"President Park was elected with a different vision for the possibilities of peace and we honour that vision ... and we hope that vision is the one that will actually take hold here," he said.
In another sign of US hopes of defusing tensions, Kerry did not visit the truce village of Panmunjom, a common stop for foreign leaders visiting Seoul.
In a joint statement released just before Kerry left Seoul, the United States said it welcomed the "trust building process" proposed by Park.
Kerry was to meet China's new President Xi Jinping and Premier Li Keqiang later Saturday.
Without naming any countries, Xi said recently that "no one should be allowed to throw a region and even the whole world into chaos for selfish gains".
After China, Kerry heads to Japan which is also deeply involved in the North Korea issue and which deployed Patriot missiles around Tokyo this week as anticipation of a missile launch by the North's mounted.
Kerry said he hoped China, Japan and the United States would be able to find the "unity" required to offer a "very different set of alternatives for how we can proceed and ultimately how we can defuse this situation".