WASHINGTON -- U.S. Secretary of State Condoleezza Rice has issued a tough warning to North Korea that the United States is well able to defend itself and its allies against nuclear and missile threats.

And South Korea on Tuesday dismissed claims that North Korea is preparing to conduct an underground nuclear test, Yonhap news agency reported.

South Korea's Defense Minister Yoon Kwang-ung told reporters in Seoul: "We've not yet seen any signs (of a nuclear test)."

He was responding to a report in the Chosun Ilbo newspaper that claimed the United States had told South Korea that U.S. intelligence authorities recently detected signs North Korea was preparing for an underground test in the northeastern region of the isolated communist state.

Earlier, Deputy Foreign Minister Song Min-soon had dismissed the possibility of North Korea conducting a nuclear weapons test in the near future.

Also on Monday, Rice -- responding to North Korea's apparent launch of a short-range missile into the Sea of Japan on Sunday -- said in Washington: "I don't think there should be any doubt about our ability to deter whatever the North Koreans are up to."

Rice told reporters: "This is not just between the United States and North Korea."

Sunday's short-range missile launch is the latest twist in a string of incidents over the past week that has refocused international attention on the nuclear standoff in the Korean peninsula.

White House Chief of Staff Andrew Card told CNN Sunday, "It appears that there was a test of a short-range missile by the North Koreans, and it landed in the Sea of Japan."

State Department spokesman Curtis Cooper issued a statement saying the test apparently took place Sunday.

"We are continuing to look into this," he said. "We are consulting closely with governments in the region. We have long been concerned about North Korea's missile program and activities, and urge North Korea to continue its moratorium on ballistic missile tests."

Card, on "Late Edition with Wolf Blitzer," said, "We're not surprised by this. The North Koreans have tested their missiles before. They've had some failures."

North Korea tested missiles in 2003, and in 1998 it test-fired a missile over Japan into the Pacific Ocean. Both triggered a great deal of concern in Japan.

Card said the United States was working to restart stalled six-party talks aimed at reaching an accord, which began in 2003 but have yielded no breakthrough.

"We have to work together with our allies around the world -- especially the Japanese, the South Koreans, the Russians and the Chinese -- to demonstrate that North Korea's actions are inappropriate," he said. "We don't want them to have any nuclear weapons, we don't want the Korean peninsula to have any nuclear weapons on it."

But Sen. Carl Levin, the top Democrat on the Armed Services Committee, told "Late Edition" the latest test showed the U.S. refusal to hold talks directly with Pyongyang was leading to an even greater nuclear threat.

In addition to the multilateral talks, Levin said, the Bush administration should "talk directly to the North Koreans. That's what's been missing. ... It has led to real failure in these policies. The nuclear threat is increasing from North Korea as a result."

Sen. Norm Coleman, a Republican and member of the Foreign Relations Committee, said North Korea lied to the United States in the bilateral talks during the Clinton presidency.

Rice said North Korea's missile program should be put on the agenda when and if the talks were resumed, AP reported.

Japanese Foreign Minister Nobutaka Machimura said after a 40-minute meeting with Rice at the State Department that they hoped China would try harder to get six-party negotiations resumed.

The United States, Japan, China, South Korea and Russia hope to negotiate an end to North Korea's nuclear program in exchange for security assurances and economic benefits.

Talks were supposed to be resumed last September, but North Korea withdrew its promise to attend. Since then, North Korea and the United States have been exchanging angry rhetoric.