Kennebunkport, Maine ? President Bush said the assassination Saturday of an Afghan vice president left the United States “more resolved than ever” to help build stability in that country.

Bush speculated that terrorists were behind the killing of Vice President Abdul Qadir and his driver in the capital city of Kabul, where U.S.-led forces last year ousted the al-Qaida-allied Taliban regime.

“It could be that. It could be drug lords. It could be longtime rivals. Who knows? All we know is a good man is dead and we mourn his loss,” Bush said.

A member of his National Security Council staff was in touch with Afghan President Hamid Karzai immediately after the killing, and Bush said his administration stands ready to assist in the Afghan investigation if Karzai asks for help.

“We are more resolved than ever to bring stability to the country so that the Afghan people can have peace and hope,” Bush said.

State Department spokesman Richard Boucher condemned the assassination of “an Afghan patriot.” Boucher’s statement said the killing “should not be allowed to divert the government and people of Afghanistan from the path of reconstruction.”

Bush expressed America’s condolences to “the government and the people of Afghanistan who lost their good and valued friend.”

“The administration and our country mourns the loss of a man who desired freedom and stability for a country he loved,” Bush said.

The president spoke with reporters after an early-morning round of golf with his father to celebrate Bush’s 56th birthday.

Bush had spoken with Karzai just one day earlier, telephoning him to discuss the U.S. military air attack that killed scores of Afghans in the central Uruzgan province on Monday.

Following a preliminary investigation, U.S. military officials admitted for the first time Saturday that civilians died in the attack.

“I would say to the Afghan people exactly what I told Chairman Karzai: anytime innocent life is lost we’re sad. Our country values life, all life and we’ll find out what the facts are,” Bush said.

Qadir was appointed one of three vice presidents during last month’s Afghan grand council, or loya jirga. He also served as governor of eastern Nangarhar province and played a leading role in ousting the Taliban.

Bush said he has not lost hope for stability there. “I am confident and I believe Chairman Karzai is confident that, with patience and with aid and with a proper strategy, Afghanistan can develop into a peaceful and hopeful nation,” he said.