The US and Japan have expressed "deep concern" over North Korea's refusal to negotiate over its nuclear weapons programme.
The US and Japan hope China will coax North Korea back to talks
US Secretary of State Condoleezza Rice and Japanese Foreign Minister Nobutaka Machimura jointly urged North Korea to return to six-party talks.
A North Korean official had earlier said his government no longer wanted even bilateral discussions with the US.
The US and Japan hope China will manage to coax North Korea back to the table.
Ms Rice, US Defence Secretary Donald Rumsfeld and their Japanese counterparts issued a joint statement in Washington of their "deep concern" over North Korea's position.
"It really is time for the North Koreans to take seriously that concern [by] returning to the six-party talks," Ms Rice said.
"The North Koreans are continuing to bring about their own isolation by not dealing with this problem."
The parties would consider "other measures" against North Korea if the negotiations collapsed completely, Ms Rice said, without specifying what they might be.
Mr Machimura said: "Should we let time slip by, then I think it will only worsen the situation because I am sure that the international community will then become tougher vis-a-vis North Korea."
He urged an "early and unconditional resumption" of the talks, which also involve China, South Korea and Russia.
Earlier this month, North Korea confirmed it had nuclear weapons and withdrew from discussions with its neighbours and the US.
It had been demanding direct negotiations with the US for two years, until Saturday's announcement by a North Korean foreign ministry official.
Speaking to China's Xinhua news agency, the official said Pyongyang no longer wanted even bilateral talks with the US, citing what he described as Washington's persistent attempts to topple the communist regime.
Meanwhile, an envoy from China, North Korea's closest ally, arrived in Pyongyang for three days to urge the country to return to six-party negotiations.
The US and Japan said they were counting on China, which has hosted the previous three rounds of talks, to play "a central role" in bringing North Korea back to the table.
But at the same time, they said they were keeping a wary eye on China's military build-up, and raised Taiwan as a mutual security concern.
They stated they had a shared goal to "encourage the peaceful resolution of issues concerning the Taiwan Strait through dialogue".
China, which views Taiwan as part of its territory, has threatened to invade the island if it ever declares formal independence.
Mr Rumsfeld and Japanese Defence Agency chief Yoshinori Ono reaffirmed their countries' alliance, which they said provided peace and stability in the region.