"Statements are one thing, real action is another," a State Department official said as he underlined the need for caution over Kim's remarks.

South Korean Unification Minister Chung Dong-Young told reporters after talks with Kim in Pyongyang earlier Friday that the leader told him North Korea could return to the six-party talks in July if Washington "recognizes and respects" his country as a dialogue partner.

Kim was also quoted saying Friday that North Korea would rejoin the nuclear Non-Proliferation Treaty (NPT) and open up to international inspectors once the nuclear standoff with the outside world was resolved.

"Let's just put it in the proper perspective. It is statement for public consumption," said the State Department official, speaking on condition of anonymity.

Even if what Kim exactly stated was the truth, "until there is a little bit more meat to the bones, we are not going to start jumping up and down and waving arms," the official said, adding there should be, for example, "signs from the Chinese that there is really something in the works."

Deputy State Department spokesman Adam Ereli said Washington was trying to confirm what Kim reportedly said with South Korea, one of the countries in the six-party talks which also involved North Korea, the United States, China, Russia and Japan.

"We've seen the reports. We certainly look forward to speaking to our friends and partners from South Korea to get a full readout of the minister's meetings in North Korea," he said.

North Korea became the first country to withdraw from the NPT in January 2003, three months after Washington accused Pyongyang of running a clandestine nuclear weapons programme based on enriched uranium. In December 2002, the Stalinist state kicked out international monitors from the International Atomic Energy Agency (IAEA).

The six-party talks hosted by China were aimed at weaning North Korea away from nuclear arms under an aid-for-disarmament proposal led by the United States.

North Korea has rejected the plan and refused to attend the fourth round of the talks in September 2004, citing what it called hostile US policy.

Asked whether the United States was optimistic over Kim's statement, Ereli said: "These are based on reports. I don't want to engage in optimism or pessimism. Let's be realistic.

"The real issue for us is getting back to the talks, but more than that engaging seriously and substantively on our proposal and on discussions to end the North Korea's nuclear programme and address the threat that faces the Korean Peninsula.

"So reports aside, the bottom line we're looking for and I think that is important is actually getting back to the talks and engaging substantively," Ereli added.

Chung had an unexpected face-to-face meeting with Kim for 150 minutes during a visit to Pyongyang in which he headed a South Korean government delegation to celebrate the fifth anniversary of a landmark inter-Korean summit.

The meeting came one week after a summit between Bush and South Korean leader Roh Moo-Hyun at the White House at which the two leaders appealed to Pyongyang to end its boycott of dialogue.

Chung quoted Kim as denying North Korea had ever said it would abandon the six-party disarmament forum, which has been stalled for a year.

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