The United States on Thursday vowed a fresh strategy to counter the North Korean nuclear threat, admitting that all previous efforts had failed.
During a visit to Japan at the start of an Asian tour, Secretary of State Rex Tillerson said he would urge China to play its part in reining in its neighbour.
In his first foray into crisis diplomacy, the new US envoy wants to reassure key Asian allies that Washington stands with them in the face of the accelerating nuclear and missile threats.
But he warned that past policies and punishments have had virtually no effect on Pyongyang's ambitions.
"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 told a press conference with Japan's Foreign Minister Fumio Kishida.
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 international sanctions, and last week test fired a salvo of ballistic missiles that fell in waters off Japan.
"In the face of the ever-escalating threat it is clear that a new approach is required," Tillerson said, offering no details.
But he reiterated Washington's vow to face down the North Korean threat and back regional friends Japan and South Korea.
"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.
Kishida and Abe thanked the former oil man for the US backing, and the Japanese prime minister fondly remembered a golf round last month with Trump.
- 'Bring it out' -
After Tokyo, Tillerson flies to Seoul for talks with South Korea's acting leader and at the weekend heads to Beijing to finalise plans for Chinese leader Xi Jinping to visit Trump in April.
US officials have been spooked by North Korea's accelerating progress towards building an intercontinental ballistic missile that could threaten US mainland cities.
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 of Beijing. "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.
It called last week for North Korea to suspend its nuclear and missile activities in exchange for the US and South Korea halting military exercises to avert a dangerous confrontation -- the latter rejected by the US.
Chinese foreign ministry spokeswoman Hua Chunying said at a briefing Thursday that Beijing stood by the idea.
"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 Kishida, observers see several options.
They include a pre-emptive strike against missile and nuclear facilities, dialogue the US has currently made conditional on tangible commitment by Pyongyang to stop the programmes, and stepped-up sanctions, according to James Kim from the Seoul-based Asan Institute of Policy Studies.
"The US Congress has shown great interest in tougher sanctions," Kim said. "That means the US could implement stronger sanctions which could be, in my view, similar to those previously imposed on Iran."
Iran came to an agreement with world powers to rein in its nuclear program after US secondary sanctions punished European banks that were dealing with the Tehran regime.
Some Washington policy experts have called for similar measures to deal with Chinese banks working with North Korea, but others hope Beijing will come on board without a clash.