U.S. Secretary of State John Kerry on Sunday stressed the United States is willing to engage with North Korea as long as it takes steps to give up nuclear weapons.
He also vowed Washington would protect its Asian allies against any provocative acts by the North, but said it wants a peaceful solution to rising tensions in the region.
"We are prepared to reach out but we need (the) appropriate moment, appropriate circumstance," Kerry told a small group of reporters, adding that North Korea had to take steps toward giving up its nuclear programs.
"They have to take some actions. Now how many and how much I want to have a discussion with folks back in Washington (about)... but they have to take action," he added.
The North has threatened for weeks to attack the United States, South Korea and Japan since new U.N. sanctions were imposed in response to its latest nuclear arms test in February. Speculation has mounted of a new missile launch or nuclear test.
"I think it is really unfortunate that there has been so much focus and attention in the media and elsewhere on the subject of war, when what we really ought to be talking about is the possibility of peace. And I think there are those possibilities," Kerry earlier told a news conference in Tokyo after a meeting with his Japanese counterpart, Fumio Kishida.
Kerry was in Japan for the final stop on an Asian tour aimed at solidifying support for curbing North Korea's nuclear programme, and reassuring U.S. allies.
Kerry said the United States would "do what was necessary" to defend its allies Japan and South Korea, but added: "Our choice is to negotiate, our choice is to move to the table and find a way for the region to have peace."
Here's the Real Danger With North Korea
Kerry also sought to clarify his comments made in Beijing on Saturday, which some took to suggest he might be offering to remove recently boosted missile defense capabilities in Asia if China persuaded North Korea to abandon its atomic programs.
The Pentagon in recent weeks has announced plans to position two Aegis guided-missile destroyers in the western Pacific and a Terminal High Altitude Area Defense (THAAD) missile defense system in Guam.
"The president of the United States deployed some additional missile defense capacity precisely because of the threat of North Korea. And it is logical that if the threat of North Korea disappears because the peninsula denuclearizes, then obviously that threat no longer mandates that kind of posture. But there have been no agreements, no discussions, there is nothing actually on the table with respect to that," Kerry said.
"Take the Money and Run"
Kerry said he might consider using someone other than an official U.S. government envoy to reach out to the North and he left the door open to a negotiation with the North that might not require them to take denuclearization steps in advance.
"If the Chinese came to us and said, 'look, here's what we've got cooking and so forth,' I'm not going to tell you that I'm shutting the door today to something that's logical and that might have a chance of success," he said. "On the other hand, what the standard is today is they have to take action."
Sen. John McCain, a Republican, voiced skepticism about the resuming negotiations with the North.
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"If we give them food, if we give them oil, if we give them money, they will come around and they take our money and run," he said.
Japan's Kishida told the same news conference that the two allies want Pyongyang to abandon its nuclear ambitions.
"We agreed that North Korea should cease provocative speech and behavior and show it is taking concrete action toward denuclearization," he said. "We cannot allow North Korea in any way to possess nuclear weapons."
North Korea Unbending
Pyongyang, which was preparing to celebrate the birth date of state founder Kim Il-Sung on Monday, reiterated it had no intention of abandoning its atomic arms programs.
"We will expand in quantity our nuclear weapons capability, which is the treasure of a unified Korea ... that we would never barter at any price," Kim Young-nam, North Korea's titular head of state, told a gathering of officials and service personnel applauding Kim Il-Sung.
The KCNA news agency also rejected as a "cunning trick" South Korean President Park Geun-hye's suggestion last week of holding talks with the North.
The South Korean capital, Seoul, displayed the calm it has shown throughout the crisis. Residents strolled in bright sunshine a day after the city's World Cup stadium was jammed with 50,000 mostly young fans of local rapper Psy.
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On Saturday, Kerry met leaders in China, the North's sole diplomatic and financial benefactor, and said China and the United States were committed to "the denuclearization of the Korean peninsula in a peaceful manner".
During his first stop in South Korea, where the United States has 28,000 troops stationed, Kerry said North Korea, furious at joint U.S.-South Korean military drills, would be making a "huge mistake" if it were to launch a missile.
He also said China was in a position to influence the North's policy and had to put "some teeth" into efforts to persuade Pyongyang to alter its policies.
Japan, separated from North Korea by less than 1,000 km (625 miles) of water and a frequent target of its anger, is well within range of North Korea's medium-range missiles.
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Japanese news reports said Tokyo had sent Aegis-class destroyers capable of missile interception to the Sea of Japan. Patriot Advanced Capability-3 interceptor missiles have been deployed at key locations in the capital and surrounding areas.
Kerry's agenda in Tokyo also included Japan's territorial disputes with China, and the future of U.S. bases in Japan.
He repeated that while Washington took no position about the ultimate sovereignty of tiny isles in the East China Sea claimed by both China and Japan, the United States "opposed any unilateral action that would somehow change the status quo".
A flare-up of the territorial row has raised fears of an unintended military incident near the islands, known as the Senkaku in Japan and the Diaoyu in China. The United States says the islets fall under a U.S.-Japan security pact, but is keen to avoid a clash in the economically vital region.