US Secretary of State Condoleezza Rice has called on North Korea to return immediately to talks aimed at halting its nuclear weapons programme.
North Korea says it has nuclear weapons
She made the comment in Japan - the latest stage of her Asian tour.
North Korea, which says it possesses nuclear arms, withdrew from six-party negotiations last month.
Pyongyang says Ms Rice must apologise for her earlier description of the country as an "outpost of tyranny", before it considers resuming talks.
Since 2002, three rounds of discussions involving the US, Russia, the two Koreas, Japan and China have sought to ease nuclear tensions on the Korean peninsula, with little success.
The US has said Korea should dismantle its nuclear weapons as part of any deal. But Pyongyang says it needs its arsenal to defend itself.
In her speech at a Tokyo university, Ms Rice said the US had "no intention of attacking or invading North Korea".
Washington was prepared to offer multilateral security assurances to Pyongyang if it agreed to end its nuclear programme, she said.
The secretary of state urged China and other regional powers to put pressure on the North.
"All parties must magnify their efforts" to convince North Korea "the time has come for decision", she added.
The BBC's Charles Scanlon in the region says China is seen as the key to a diplomatic solution to the North Korean issue, and that US officials feel it is not using enough leverage with its communist ally.
Beijing, for its part, has repeatedly called for more flexibility from the US.
Ms Rice's remarks coincide with the start of a week of joint exercises between South Korean and US troops.
About 17,000 American personnel are taking part in the annual event - a number similar to recent years.
North Korea described the exercises as "extremely dangerous", and said they justified its decision to boost what it called its defensive nuclear arsenal.
In her wide-ranging address in Tokyo, Ms Rice also set out US policy in the Asia-Pacific region.
She urged Beijing to pursue greater democracy: "Even China must eventually embrace some form of open, genuinely representative government if it is to reap the benefits and meet the challenges of a globalising world."
She said Washington stood by its policy of advising Taiwan not to seek full independence.
Ms Rice is due to have a series of meetings in Japan. She has already stopped in Afghanistan, India and Pakistan, and will travel on to South Korea and China.