SEOUL, South Korea – A supercarrier sent jets into overcast skies Tuesday in U.S.-South Korean military drills that North Korea warned could spark war, but signs of diplomacy emerged alongside the tensions over last week’s deadly North Korean attack.

The North’s only major ally, China, hosted a top North Korean officialfor talks, and Japan also planned to send an envoy to China. The U.S., South Korea and Japan agreed to talk next week in Washington about the North’s nuclear weapons and its Nov. 23 artillery barrage that killed four South Koreans.

It was unclear if the Beijing visit by North Korea’s Choe Thae Bok, chairman of the North’s Parliament, would lead to any diplomatic solution. China, under pressure to rein in its ally, proposed emergency regional talks earlier this week, but South Korea, the United States and Japan gave a cool response.

Even as diplomats scrambled, leaked U.S. diplomatic cables revealed signs of a rift in the relationship between China and North Korea, a striking contrast from official statements underscoring their strong historical ties.

Documents from the whistle-blowing website WikiLeaks showed China’s frustration with the North and speculated that Beijing would accept a future Korean peninsula unified under South Korean rule.

The North, meanwhile, reminded the world it was forging ahead with its nuclear efforts. Pyongyang said Tuesday that it’s operating a modern uranium enrichment plant equipped with thousands of centrifuges. The main Rodong Sinmun newspaper said in an editorial that the North is also building a light-water reactor.

The North first revealed the uranium program in early November to a visiting American scientist. A light-water nuclear power reactor is ostensibly for civilian energy purposes, but it gives the North a reason to enrich uranium. Uranium enrichment would give the North a second way to make nuclear bombs, in addition to its known plutonium-based program.

North Korea has pushed for renewed international talks on receiving much-needed aid in return for commitments to dismantle nuclear programs, and its recent aggression could reflect frustration that those talks remain stalled.

The North unleashed an artillery barrage last week on a South Korean island that hit civilian areas, marking a new level of hostility along the contested maritime border between the Koreas. The attack killed two civilians and two marines.

In a major address Monday, South Korean President Lee Myung-bak pledged a tough response if the North carries out any further attacks.

Kim Keun-sik, a North Korea analyst at South Korea’s Kyungnam University, said sides in the standoff will have competing ideas on how to resolve tension.

“North Korea and China will want to resolve the matter through a dialogue,” he said, “while South Korea and the U.S. will say ‘Why negotiate at this time?’ and think about pressure and punitive measures” on the North.

The Wikileaks documents further complicate the diplomatic picture.

China, the documents show, “would be comfortable with a reunified Korea controlled by Seoul and anchored to the US in a ‘benign alliance’ as long as Korea was not hostile towards China,” then-South Korean vice-foreign minister, Chun Yung-woo, is quoted as telling U.S. ambassador to South Korea Kathleen Stephens in February.

Chun predicted the government in Pyongyang would last no more than three years following the death of ailing leader Kim Jong Il, who is seeking to pass power to son Kim Jong Un, an untested political newcomer in his 20s.

In Seoul, government officials declined to comment on Chun’s reported comments.

During Tuesday’s U.S.-South Korean military drills, a heavy fog engulfed the USS George Washington supercarrier. The carrier’s fog horn boomed out as U.S. aircraft took off and landed in quick succession.

Cmdr. Pete Walczak said the ship’s combat direction center was closely monitoring any signs of ships, aircraft of any other activity and that nothing unusual was detected from North Korea.

“Absolutely nothing,” Walczak said. “A lot of saber-rattling, fist-shaking, but once our presence is here, reality says that it’s really nothing.”

The North’s propaganda machine warned that the drills could trigger a “full-blown war” on the peninsula. “Our republic has a war deterrent that can annihilate any aggressor at once,” the government-run Minju Joson said.

On the streets of the North Korean capital, Pyongyang, North Koreans spoke with pride of their military.

“Those who like fire are bound to be punished with fire,” Kim Yong Jun, a Pyongyang resident, told international broadcaster APTN.

A rally in Seoul, meanwhile, drew several thousand protesters who burned North Korean flags and called for the overthrow of Kim Jong Il. “We’ve had enough,” said Kim Jin-gyu, 64, adding that North Korea deserves punishment. “We should just smash it up.”

Yonhap news agency reported that Choe, the North Korean official, was expected to meet top Chinese communist party officials and discuss last week’s artillery barrage, the North’s nuclear program and the U.S.-South Korean military drills.

China has sought to calm tensions by calling for an emergency meeting among regional powers involved in six-party nuclear disarmament talks — the two Koreas, the U.S., China, Russian and Japan — which have been stalled since last year.

Seoul, however, wants proof of Pyongyang’s commitment to denuclearization as well as a show of regret over the March sinking of a warship.

Japan rejected a new round of aid-for-disarmament talks any time soon, but announced Tuesday that a nuclear envoy would travel to China. Tokyo provided no further details

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Santana and Kelly Olsen reported from aboard the USS George Washington. AP writers Foster Klug, Kim Kwang-tae and Ian Mader in Seoul, Christopher Bodeen in Beijing, and photographer Jin-man Lee in Yeonpyeong contributed to this report.