WASHINGTON -- Secretary of State Hillary Rodham Clinton said she regards the greatest threat to the United States to be weapons of mass destruction in the hands of an international terrorist group.

"The biggest nightmare that many of us have is that one of these terrorist member organizations within this syndicate of terror will get their hands on a weapon of mass destruction," Ms. Clinton told CNN's "State of the Union" program in a taped interview broadcast Sunday. That's "the most, yes, threatening prospect we see," she said.

Since the Sept. 11, 2001, attacks in the U.S., the al-Qaida terrorist network has become "more creative, more flexible, more agile," Ms. Clinton said, according to a transcript of the interview. "They are unfortunately a very committed, clever, diabolical group of terrorists who are always looking for weaknesses and openings."

A nuclear-armed North Korea or Iran "poses both a real or a potential threat," Ms. Clinton said. "But I think that most of us believe the greater threats are the transnational non-state networks. Primarily the extremists -- the fundamentalist Islamic extremists who are connected to al-Qaida in the Arab peninsula."

North Korea has detonated two nuclear devices and tested several missiles. The communist regime has said it isn't willing to return to multilateral nuclear disarmament talks while the country is subject to United Nations sanctions.

Asked if she was convinced that Iran had a nuclear weapon, Ms. Clinton said "no," acknowledging there is "some debate" over how close they may be to developing a weapon.

The U.S., its European allies and United Nations inspectors suspect Iran is using its uranium enrichment program to build a nuclear bomb. The U.S. wants more United Nations sanctions aimed at halting the program, which Iran, with the world's second-biggest oil and natural gas reserves, says is for peaceful uses such as power generation.

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