The US and South Korean navies on Wednesday wrapped up war games meant as a muscular show of force to North Korea, as world powers remained sharply divided over how to deal with the nuclear-armed regime.
Their biggest-ever joint exercise, which saw jet fighters thunder through the sky above a US carrier battle group, began days after Pyongyang stunned the world with a deadly artillery strike on a South Korean island.
The shelling of Yeonpyeong island, which killed two marines and two civilians, infuriated South Koreans and sharply raised public support for a far tougher military response if the volatile North should attack again.
The 10 warships and 7,300 crew taking part in the drill on Wednesday carried out 'manoeuvres of fleet protection and logistic sustainment under various scenarios of enemy threat', said South Korea's Joint Chiefs of Staff.
They also said both sides were planning more drills this month or in early 2011, although no details had been finalised yet.
The North has warned that the four-day Yellow Sea exercises brought the Koreas closer to 'the brink of war'. In the South, Defence Minister Kim Tae-Young said there was 'ample possibility' of another North Korean strike.
The regime of Kim Jong-Il, which has staged two atomic bomb tests since 2006, ramped up tensions when it boasted on Tuesday about a new nuclear facility that, experts warn, could be used to produce weapons-grade uranium.
With the Korean peninsula plunged into its worst crisis in years, diplomats at the United Nations and elsewhere struggled to find common ground on whether to punish Pyongyang or seek to engage it in new talks.
Diplomats said China, the long-time patron of the communist regime, has blocked attempts for a UN Security Council condemnation of North Korea over its attack and its new nuclear activities, which contravene UN resolutions.
"Council talks have come to a standstill. It is now very likely that the Security Council will do nothing about North Korea," one said.
Beijing has instead proposed that the six parties to long-stalled North Korean denuclearisation talks - the two Koreas, the United States, China, Russia and Japan - hold an emergency meeting on the crisis.
Washington, Seoul and Tokyo have been cool to the proposal or rejected it.
White House spokesman Robert Gibbs told reporters: "I think the Chinese have a duty and an obligation to greatly press upon the North Koreans that their belligerent behaviour has to come to an end.
"And I think you'll see progress on multilateral discussions around this over the next few days."
Diplomats are seeking to arrange a meeting between US Secretary of State Hillary Clinton and the South Korean and Japanese foreign ministers, though no date has been announced yet.
Envoys from North Korea and Japan are now visiting Beijing, and China's top foreign policy official Dai Bingguo was expected to head to North Korea this week, according to reports.
Russia's deputy nuclear envoy Grigory Logvinov was due in Seoul on Wednesday to meet South Korea's chief nuclear envoy Wi Sung-Lac. Moscow has had friendly ties with Pyongyang but has said its attack last week deserves to be condemned.
The frantic diplomacy is going on against the backdrop of a massive leak of US embassy cables by whistle-blower site WikiLeaks, which adds a new perspective on China's views about North Korea.
China has long supplied the impoverished country with food, energy and diplomatic cover, in part because it fears a regime collapse that would bring a flood of refugees and erase a buffer state with the US-allied South.
But the leaked US cables - although they are second - and third-hand accounts of Chinese officials' views - nonetheless suggest Beijing is growing more exasperated with its neighbour.
The sensitive cables also reflected a view that China may be growing more open to the North eventually being absorbed by the South.
The spike in tensions comes as North Korea's Kim, 68, is thought to be in poor health and readying to hand over power to his youngest son Kim Jong-Un, who two months ago assumed a top military post at the age of 27.