President Bush on Thursday warned North Korea against transferring nuclear weapons or material to other countries, saying such an act would be considered a "grave threat" to the United States.

The standoff over North Korea's nuclear weapons program is atop the agenda in most of the meetings the president will have during his eight-day, three-nation Asian trip, which kicked off with a speech in Singapore.

"The transfer of nuclear weapons or material by North Korea to states or non-state entities would be considered a grave threat to the United States and we would hold North Korea fully accountable for the consequences of such action," Bush said in the speech at the National University of Singapore.

Ahead of its Oct. 9 nuclear test, North Korea pledged not to launch a first strike or allow its bomb technology to be spread outside the country.

Bush also urged allies in the region to stand firm against a nuclear-armed North Korea and enforce U.N. sanctions against the country for conducting a nuclear weapon test last month.

"For the sake of peace, it is vital that the nations of this region send a message to North Korea that the proliferation of nuclear technology to hostile regimes or terrorist networks will not be tolerated," he said.

Bush leaves Friday for Vietnam where he will attend the summit of the 21-member Asia Pacific Economic Cooperation forum. On Thursday, APEC foreign ministers including U.S. Secretary of State Condoleezza Rice discussed a "carrots and sticks" approach to pressure North Korea to drop its nuclear weapons program.

They also expressed the hope that the six-party talks — involving China, Japan, Russia, the two Koreas and the U.S. — will make genuine progress in ending North Korea's development of nuclear weapons.

Bush said the five nations involved in talks with North Korea "are speaking with one voice."

"The only way for North Korea to move forward, for the good of their people, is to abandon its nuclear weapons programs and rejoin the international community," he said.

The president described as "encouraging" North Korea's announcement on Oct. 31 that it was prepared to return to the negotiating table after a one-year boycott.

"The United States wants these talks to be successful, and we will do our part," Bush said. "Ultimately, the success of these talks depends on the regime in North Korea. Pyongyang must show it's serious."

He said if North Korea chooses a peaceful path, America and the other nations in the six-party talks are prepared "to provide security assurances, economic assistance and other benefits to the North Korean people.

The six-nation talks stalled a year ago when North Korea walked out over penalties imposed by the United States for alleged illegal activities by its government, including counterfeiting and money laundering.

With China's influence on the rise and his own stature weakened at home after his Republican Party lost midterm elections to anti-war, anti-free trade Democrats, Bush sought to ease any doubts in the region about Washington's long-term commitment. He assured Asian leaders that the U.S. engagement of Asia will not diminish.

Bush said the United States will remain a reliable partner in liberalizing trade, confronting North Korea's nuclear threat and fighting terrorism, poverty and disease.