President Bush has left Singapore and is headed to the Vietnamese capital, Hanoi, for a summit of Asia-Pacific leaders.
Mr. Bush is expected to meet with Vietnamese President Nguyen Minh Triet and other Vietnamese officials later on Friday, and then he will have dinner with leaders of the 21-nation Asia-Pacific Economic Cooperation forum.
President Bush will attend the APEC summit on Saturday and Sunday.
Vietnam is Mr. Bush's second stop on an six-day, three-nation tour of Southeast Asia.
On Thursday in Singapore, he pledged the United States will remain engaged in the region to help boost prosperity and security there. In a speech at the National University of Singapore, he also said America's interests depend on what he called "the expansion of freedom and opportunity" along the Pacific Rim.
Mr. Bush said North Korea is one of the biggest security threats in the region. He urged regional leaders to make clear to Pyongyang it will not be allowed to transfer nuclear weapons or other sensitive materials to hostile regimes or terrorist groups.
President Bush is visiting Vietnam for the first time. He is the second U.S. president to go to the country following the end of the Vietnam War in 1975. President Clinton traveled to Vietnam in 2000.
Mr. Bush will also visit Indonesia during his trip. He returns to Washington late Tuesday after stopping in Hawaii to meet with U.S. troops.
U.S. Secretary of State Condoleezza Rice is accompanying Mr. Bush to Vietnam and Indonesia, and will lead the U.S. delegation at the APEC summit.