North Korea has a clear course of action available to it, and will find "ready partners" in the United States if it follows through, U.S. Secretary of State John Kerry told reporters.
Japan's foreign minister, Fumio Kishida, who appeared with Kerry at a news conference, was more explicit, saying that North Korea must honor its commitment to earlier deals regarding its nuclear and missile programs and on returning kidnapped foreigners.
The officials agreed on the need to work toward a nuclear-free North Korea and opened the door to direct talks if certain conditions are met.
Their comments highlight the difficulty in resolving the North Korean nuclear situation in a peaceful manner, as pledged by Kerry and Chinese leaders in Beijing on Saturday.
Gaining China's commitment, Kerry insisted, was no small matter given Beijing's historically strong military and economic ties to North Korea.
The issue has taken on fresh urgency in recent months, given North Korea's tests of a nuclear device and intercontinental ballistic missile technology, and its increasingly brazen threats of nuclear strikes against the United States.
U.S. and South Korean officials believe the North may deliver another provocation in the coming days with a mid-range missile test.
"The question," Kerry said, "is what steps do you take now so we are not simply repeating the cycle of the past years." That was a clear reference to the various negotiated agreements and U.N. Security Council ultimatums that North Korea has violated since the 1990s.
"We have to be careful and thoughtful and frankly not lay out publicly all the options," Kerry said.
Given their proximity and decades of hostility and distrust, Japan and South Korea have the most to fear from the North's unpredictable actions.
Kerry said the U.S. would defend both its allies at all cost.
He also clarified a statement he made Saturday in Beijing, when he told reporters the U.S. could scale back its missile-defense posture in the region if North Korea goes nuclear-free.
It appeared to be a sweetener to coax tougher action from China, which has done little over the years to snuff out funding and support for North Korea's weapons of mass destruction program.
China fears the increased U.S. military presence in the region may be directed at it as well.
Kerry said America's basic force posture wasn't up to debate. "There is no discussion that I know of to change that," he said.
But he said it was logical that additional missile-defense elements, including a land-based system for the Pacific territory of Guam, deployed because of the Korean threat could be reversed if that threat no longer existed.
"There's nothing actually on the table with respect to that. I was simply making an observation about the rationale for that particular deployment, which is to protect the United States' interests that are directly threatened by North Korea," Kerry said.
Kerry's visit to Japan followed two days of meetings in South Korea and China.
Six-nation talks with North Korea collapsed more than four years ago, and Kerry said that for negotiations to resume, North Korea "needed to indicate their willingness to move toward denuclearization."
"They have to take some actions," he said. "How many or how much? I'd have to talk to folks back in Washington about that. But if the Chinese came to us and said, 'Look, here's what we have cooking,' I'm not going to tell you I'm shutting the door today to something that's logical and might have a chance of success."
At round-table session with U.S. journalists, Kerry said that under the right circumstances, he even would consider making a grand overture to North Korea's leader, such as an offer of direct talks with the U.S.
"We're prepared to reach out," he said.
Kerry said diplomacy required risk-taking and secrecy such as when President Richard Nixon engaged China in the 1970s or U.S. back-channel talks were able to end the Cuban missile crisis a decade earlier.
"I'm not going to be so stuck in the mud that an opportunity to actually get something done is flagrantly wasted because of a kind of predetermined stubbornness," Kerry told reporters.
"You have to keep your mind open. But fundamentally, the concept is they're going to have to show some kind of good faith here so we're not going to around and around in the same-old same-old."