U.S. Secretary of State Rex Tillerson hinted Thursday at a tougher strategy to confront North Korea's nuclear threat, but said Pyongyang had no need to fear the United States, an alternately threatening and reassuring message that suggests the Trump administration is still formulating a clear policy.

In Japan at the start of a three-country Asia tour, Tillerson offered no details about what would form the "different approach" to North Korea the U.S. will pursue. He pointedly noted that 20 years of "diplomatic and other efforts" had failed to dissuade the isolated communist government from developing its nuclear program, which he called an "ever-escalating threat."

Speaking alongside Japanese Foreign Minister Fumio Kishida, Tillerson recited the long-standing U.S. demand that the North "abandon its nuclear and ballistic missile programs and refrain from any further provocation."

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Tillerson shakes hands with Japan's Foreign Minister Fumio Kishida before their meeting in Tokyo. (Toru Hanai/Reuters)

He said his visit to Asia was designed to "exchange views on a new approach," echoing the comments of others in Washington, who've said U.S. President Donald Trump wants to examine all options — including military ones — for halting the North's weapons programs before it becomes capable of developing a nuclear-tipped missile that could reach the U.S. mainland.

North Korea claims self-defence

In Beijing, a North Korean diplomat said Thursday that Pyongyang must act in self-defence against the U.S.-South Korea military drills, which he said have brought the region to the brink of nuclear war. He said the drills were aimed at using atomic weapons for a pre-emptive strike against North Korea. Washington says the manoeuvres are routine and defensive.

"The United States holds a joint military exercise every year to push the situation on the Korean Peninsula to a serious situation, and that is the source of the super tough measures we must take," Pak Myong Ho told reporters in a rare briefing at the North Korean Embassy in the Chinese capital. He spoke through a translator.

North Korea has accelerated its weapons development in violation of multiple UN Security Council resolutions and despite tough sanctions levied against it. Last year, the North conducted two nuclear test explosions and 24 ballistic missile tests. Experts say it could have a nuclear-tipped missile that could reach the United States within a few years.

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Tillerson will head to South Korea and China next. (Toru Hanai/Reuters)

Citing the continued North Korean missile launches this year, Tillerson​ said that "in the face of this ever-escalating threat it is clear that a different approach is required."

Calling on China

He said his trip was intended to get input from other governments. Tillerson will travel Friday to South Korea and then China on Saturday.

Both Tillerson and Kishida urged China use its economic leverage with North Korea to push it to change course.

During last year's election campaign, presidential candidate Donald Trump called into question U.S. security alliances and called for Tokyo and Seoul to contribute more for their defence. Tillerson, however, stressed that co-operation with Japan and South Korea was "critical."

But if Tillerson's words were meant to put Pyongyang on notice, he quickly pivoted: "North Korea and its people need not fear the United States or their neighbours in the region who seek only to live in peace with North Korea."

Possible focus on military options

U.S. State Department spokesman Mark Toner wouldn't specify Thursday what elements the new U.S. approach would entail. But he said Tillerson had sought to emphasize that the U.S. prefers a peaceful solution and that the U.S. was taking issue with North Korea's government, not its people.

Tillerson's trip, which will take him next to South Korea and China, comes as the Trump administration conducts a broad review of U.S. policy toward North Korea. Suggestions by Tillerson and others about a new direction have fuelled speculation the U.S. may put greater focus on military options, which previous administrations have avoided.

Central to the U.S. review is China and its role in any bid to persuade Pyongyang to change course. China remains the North's most powerful ally.

While the U.S. and its allies in Seoul and Tokyo implore Beijing to press its economic leverage over North Korea, the Chinese have emphasized their desire to relaunch diplomatic talks — a non-starter for the U.S. under current conditions.

The U.S. and China also disagree over U.S. deployment of a missile defence system to South Korea. The U.S. says it's a system focused on North Korea. China sees it as a threat to its own security.

State Department officials have described Tillerson's effort this week as a "listening tour" as the administration seeks a coherent North Korea policy, well co-ordinated with its Asian partners.