Ms. Rice would not comment on the substance of the assertion about North Korea by the head of the U.S. Defense Intelligence Agency, Navy Vice Admiral Lowell Jacoby.
But at a news conference after talks with Chilean President Ricardo Lagos, Ms. Rice said she is sure the North Koreans are well aware of the strong military deterrent of U.S. and South Korean forces, and she urged Pyongyang to return to the six-party talks on its nuclear program.
Speaking at a public session of the Senate Armed Services Committee Thursday, Admiral Jacoby said the assessment of U.S. experts is that North Korea has the capability to arm a missile with a small nuclear device.
The defense intelligence chief also said U.S. analysts believe North Korea has the ability to deploy a two-stage missile that could hit parts of the continental United States, an assertion that drew expressions of alarm from committee members.
News reports in recent day have also said U.S. officials are concerned North Korea might be preparing to test a nuclear device, and may have shut down its Yongbyong nuclear reactor with the apparent intention of harvesting plutonium.
In her remarks here, when asked about the Senate testimony, Ms. Rice said the North Koreans are doing all kinds of things and that U.S. experts have differing assessments about their activities.
Without being specific, she said that if North Korea engages in certain kinds of behavior, it will only deepen its isolation.
She said she hopes there is an understanding of that in Pyongyang, where she said she is confident officials have no illusions about the balance of forces in the region. "We maintain a strong deterrent on the Korean peninsula both through our alliance with South Korea and through American military power in the region. And I'm quite certain the North Koreans are not confused about the military situation on the Korean peninsula. So yes, of course we've all been troubled by developments in North Korea. That's why we have the six-party talks. But that's the way for the North Koreans to end their isolation," she said.
The Secretary of State said it is a fairly universal view that North Korea should not have nuclear weapons, and that the only way for Pyongyang to obtain the benefits it appears to want from the international community is to negotiate an end to its program through the six-party talks.
The Chinese-sponsored talks have been idle since last June, and Ms. Rice said a referral of the issue to the U.N. Security Council remains an option.
U.S. intelligence officials believe North Korea has had a nuclear weapons capability since early 1990's, and may have added to its arsenal since it expelled U.N. nuclear inspectors and withdrew from the Nuclear Non-Proliferation Treaty in 2003.
In the six-party talks, the United States has offered to be part of multi-lateral security guarantees for North Korea if it verifiably and irreversibly scrapped its weapons program.