The top U.S. arms negotiator has issued a stern reply to months of bellicose language from North Korea, saying Washington will not bow to nuclear blackmail by the Stalinist state. U.S. Undersecretary of State John Bolton also made an explicit attack on North Korean leader Kim Jong Il.

In words likely to cause outrage in Pyongyang, Undersecretary Bolton slammed North Korea for what he called nuclear blackmail, and sharply criticized leader Kim Jong Il for the political oppression and poverty that characterize his nation.

"While he lives like royalty in Pyongyang, he keeps hundreds of thousands of his people locked in prison camps with millions more mired in abject poverty. For many in North Korea, life is a hellish nightmare," Mr. Bolton said.

In 1994, North Korea agreed to end a program aimed at producing nuclear weapons, in return for various forms of aid. Last October, Washington revealed that the North had secretly gone ahead with a weapons program anyway.

Washington demanded an immediate end to the program. In response, Pyongyang has made a series of provocative gestures, saying it already possesses an undisclosed number of nuclear weapons, and implying that it might use them unless Washington agrees to sign a non-aggression pact.

Speaking in Seoul, where he is meeting with South Korean officials, Mr. Bolton said that giving in to North Korea's demands would only encourage Mr. Kim and other would-be tyrants around the world.

He noted that the Bush Administration is keeping "all options on the table" for dealing with the North Korean nuclear threat.

American officials have previously said they hope the dispute can be resolved through diplomacy, but President Bush also says the use of force is still an option.

Mr. Bolton was in Beijing earlier in the week for similar talks, and will meet Japanese leaders in Tokyo on Friday. He wants North Korea's neighbors to agree to a tough and united stance toward North Korea.

Pyongyang had its own words of criticism for the United States Thursday. The state-run newspaper Rodong Sinmun said the United States should be brought to "international justice" for using "misinformation" about Saddam Hussein's weapons of mass destruction to justify war in Iraq.

The United States, along with China, Japan and South Korea, are awaiting Pyongyang's reply to a U.S. proposal for multilateral talks on the dispute. Mr. Bolton said Thursday that the ball is now in North Korea's court, meaning Pyongyang has the chance to help end the crisis by agreeing to multilateral discussions.

The North has repeatedly said it only wants direct talks with the United States, which is blames for igniting the crisis, and which it sees as a threat to its security.