"The United States remains committed to diplomacy. The United States also reserves all options to defend our friends and our interests in the region against the threats from North Korea," Bush said at the hastily-held press conference.

The warning came after the DPRK announced Sunday night that it had successfully conducted a nuclear test.

Bush said that the United States is working with partners in the region and the UN Security Council to ensure there are "serious repercussions" for the DPRK.

"We all agree that there must be a strong Security Council resolution that will require North Korea to abide by its international commitments to dismantle its nuclear programs," Bush said, adding that the resolution should help prevent the DPRK from exporting nuclear or missile technologies.

While declaring the United States has no intention to attack the DPRK, Bush said that the United States will increase defense cooperation with its allies, including "cooperation on ballistic missile defense to protect against North Korean aggression, and cooperation to prevent North Korea from exporting nuclear and missile technologies."

Bush said he thanks China, South Korea, Japan and Russia for voicing their strong opposition to the DPRK's nuclear test.

"Peace on the Korean peninsula requires that these nations send a clear message to Pyongyang that its actions will not be tolerated, and I appreciate their leadership," Bush added.

As to Iraq, Bush vowed to stay on the course despite rising pressure from the American public to withdraw U.S. forces out of the Islamic country.

"If we are to abandon that country before the Iraqis can defend their young democracy, the terrorists would take control of Iraq and establish a new safe haven from which to launch new attacks on America," Bush said.

Bush also dismissed as "not credible" an independent U.S. study that estimated up to 655,000 Iraqis had died since the 2003 U.S. invasion.

On Iran, Bush called for international unity on Iran's nuclear issue and voiced commitment to solve it through diplomacy.

"I firmly believe that, with North Korea and with Iran, that it is best to deal with these regimes with more than one voice," Bush said, adding that "it was important to change how we approach the problem so that we could solve it diplomatically."

Bush made the comments as his administration has reached a crisis point with the DPRK, Iran and Iraq, an "axis of evil" he introduced nearly five years ago. The DPRK has claimed it conducted a nuclear test, Iran refused to halt its uranium enrichment and Iraq appears to be tipping into a civil war.

The Washington Post, citing analysts and U.S. officials, has said that each problem appears to feed on the others, making the stakes higher and requiring Bush and his advisers to make difficult calculations.