The United States has no intention of attacking North Korea, President George W. Bush said Wednesday, while calling for tough sanctions in response to the Communist country's claims to have tested a nuclear weapon.

"In response to North Korea's actions, we're working with our partners in the region and the United Nations Security Council to ensure there are serious repercussions for the regime in Pyongyang," Bush told reporters in Washington, D.C.

Bush said North Korea's claim to have detonated a nuclear bomb on Monday is a threat to international peace and security.

In a news conference at the White House, Bush said the U.S. remains committed to resolving the nuclear standoff through diplomacy but it "reserves all options to defend our friends in the region."

Bush also thanked South Korea, Russia, and China for their "strong condemnation" of North Korea's actions.

The U.S. president called for a series of measures to prevent North Korea from exporting nuclear technology and to prevent financial transactions that would help it to develop nuclear technologies.

As Bush spoke, UN Secretary General Kofi Annan urged the United States to engage in one-on-one talks with North Korea, which Washington has refused to do.

Annan said he is concerned about North Korea's reported nuclear test, its threat to conduct another test and its warning that UN sanctions would be seen as an act of war. He said these moves have stoked tensions, especially in Japan and South Korea.

"I would urge the North Korean authorities not to escalate the situation any further," Annan told reporters. "We already have an extremely difficult situation."

Pyongyang says test a success, vows more

Earlier Wednesday, North Korea's Foreign Ministry said in a statement that North Korea would respond with "physical measures" in response to any U.S. pressure.

Pyongyang said the underground test was a success and vowed to carry out more.

"If the U.S. keeps pestering us and increases pressure, we will regard it as a declaration of war and will take a series of physical corresponding measures," the ministry said in a statement carried by the official Korean Central News Agency.

"We are ready for both dialogue and confrontation."

The statement was the first formal comment from the North Korean government since the test was conducted.

It also claimed that North Korea had not broken an agreement reached at six-party talks in September, when the country said it wants to normalize relations with Western countries.

South toughens defence stance

South Korea, meanwhile, said it plans to bolster its arsenal of conventional weapons if North Korea is confirmed to have nuclear bombs.

And in a rare direct criticism of the North, South Korean President Roh Moo-hyun said he believes that Pyongyang may be exaggerating its need for security in order to justify its nuclear program.

"The security threat North Korea speaks of either does not exist in reality, or is very exaggerated," Roh said in a report by Yonhap news agency.

South Korean Defence Minister Yoon Kwang-ung said South Korea will take steps to protect itself as North Korea issues threats and conducts nuclear tests.

"If North Korea really has the [nuclear] capabilities, we will improve and enlarge the number of conventional weapons as long as it doesn't violate the principle of denuclearization," Yoon told parliament.

"We will supplement [our ability] to conduct precision strikes against storage facilities and intercept delivery means, while also improving the system of having military units and individuals defend themselves," he said.

With files from the Associated Press