Secretary of State Rex Tillerson is in Asia for his first foray into crisis management, and vowed in Japan on Thursday to press Beijing to rein in its neighbour.
But, speaking after meeting Japanese officials, he offered no new details of his plan to defuse the threat posed by Pyongyang's recent ballistic missile tests.
Now, he is due in Seoul for talks with acting president Hwang Kyo-Ahn, and on Saturday he will head to China to press a reluctant great power to back tougher sanctions.
But, before leaving Japan, he warned that past policies and punishments have had virtually no effect on Pyongyang's ambitions and that a new course was needed.
"I think it's important to recognise that the diplomatic and other efforts of the past 20 years to bring North Korea to a point of denuclearisation have failed," he said.
North Korea has a long-standing ambition to become a nuclear power and conducted its first underground atomic test in 2006, in the teeth of global opposition.
Four more test blasts have followed, two of them last year.
It has continued to defy the international community, even after two rounds of UN-backed sanctions, and last week test fired a salvo of missiles that fell in waters off Japan.
Unwavering committment
"In the face of the ever-escalating threat it is clear that a new approach is required," Tillerson said.
And he reiterated Washington's vow to back key regional allies Japan and South Korea in the event of attack.
"The US commitment to the defence of Japan and its other treaty allies through the full range of our military capabilities is unwavering," he promised.
US President Donald Trump stirred concern in the region during his White House campaign by suggesting allies like Japan and South Korea need to do more to defend themselves.
But since his victory he has twice met with Japanese Prime Minister Shinzo Abe and has been careful to offer complete support, as Tillerson reiterated.
US officials have been spooked by North Korea's accelerating progress towards building an intercontinental ballistic missile that could threaten US mainland cities.
But China is perhaps the last country with significant leverage over Kim Jong-Un's isolated regime.
"We do believe they have a very important role to play," Tillerson said. "We will be having discussions with China as to other actions that they should be undertaking."
Beijing shares US concerns over Pyongyang's attempts to build an arsenal of nuclear devices, but has also blamed Washington for escalating tensions.
Chinese foreign ministry spokeswoman Hua Chunying said at a briefing Thursday that Beijing stood by its call for a halt to joint US-South Korean exercises, to lower tensions.
"If the US or another country has a better plan, a better proposal, they can bring it out," she said.
In the absence of specific details on how to increase pressure on Pyongyang from either Tillerson or his Japanese host, observers see a range of stark options.
They include a pre-emptive strike against missile and nuclear facilities or stepped up sanctions,
But the United States could also open a dialogue with the North -- something it has currently made conditional on a tangible commitment by Pyongyang to stop the programmes.
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