Updated

A top U.S. diplomat on Friday joined South Korea in warning the communist North against conducting a nuclear test, following reports that it may be preparing its first such trial.

U.S. Assistant Secretary of State Christopher Hill (search), the U.S. envoy to North Korean disarmament talks, was in Seoul (search) after trips to Beijing and Tokyo to coordinate efforts aimed at persuading the North to return to the negotiating table.

"Often when a country announces its membership in the nuclear arms club, the next step would be a test," Hill told reporters. "To go ahead and have a nuclear test ... would be truly troubling for the talks."

On Friday, Hill met South Korean Unification Minister Chung Dong-young, responsible for Seoul's relations with the North, who a day earlier had warned the North to carefully consider before detonating an atomic bomb.

Chung said Thursday that a nuclear test would "shake the fundamentals of the framework" of the six-nation talks, and that the North "should judge and act prudently." Chung said there is no evidence the North is preparing for a test.

But his warning came after U.S. media reported over the weekend that Pyongyang might be preparing for its first nuclear test.

At Friday's news conference, Hill said that six-way talks between North Korea, its neighbors, Japan and the United States, are still the best way to resolve the nuclear dispute.

"What I don't want to do is get into discussing other options because that would undermine the six-party talks," Hill said. "All those options are not as good as the six-party talks." The talks have been stalled since last June after three inconclusive rounds.

"We are still in a situation where one of the parties is refusing to come to the table, and that of course, is North Korea," Hill said. "They have not made a strategic decision to do away with their nuclear weapons."

Hill's comments came a day after Vice Adm. Lowell Jacoby, director of the Defense Intelligence Agency, told a Senate committee in Washington that North Korea has the ability to arm a missile with a nuclear weapon, a potentially significant advance for the isolated communist state.

But two U.S. defense officials, speaking in Washington on the condition of anonymity, told The Associated Press that U.S. intelligence assessments maintain Pyongyang is several years away from developing a nuclear-armed missile powerful enough to reach the United States. North Korea has not solved all the problems of turning a nuclear device into a small warhead for an intercontinental ballistic missile, they said, citing analysts' assessments.

President Bush, at a White House news conference Thursday night, said he wanted to reach a diplomatic solution on the North's nuclear program. He said that what he wants to do is "work with our allies on this issue and develop a consensus, a common approach, to the consequences of (North Korean leader) Kim Jong Il."

Resuming the six-nation talks gained urgency in February when the North claimed it already has produced nuclear weapons and would boycott further talks. The North has since threatened to increase its nuclear arsenal, and has demanded that the United States halt what the North calls a hostile police toward Pyongyang.