The head of Usama bin Laden's Al Qaeda training camps in Afghanistan and the former Taliban ambassador to Pakistan were turned over to U.S. custody on Saturday.

U.S. forces took custody of Ibn Al-Shayk al-Libi, believed to be bin Laden's highest-ranking associate in American custody so far, at the Marine base at Kandahar airport. U.S. officials say the former Taliban ambassador to Pakistan, Abdul Salaam Zaeef, will be detained at Kandahar as well.

President Bush said Saturday that the war on terror was in "a dangerous phase" with special forces hunting for fugitive leaders in Afghanistan's dangerous terrain.

Al-Libi and Zaeef are thought to have information that could lead U.S. forces to the two most wanted men in that war.

"These are important figures: One was close to Usama bin Laden and the other was very close to (former Taliban supreme leader) Mullah Mohammed Omar," former CIA terrorism analyst Stan Beddington said Saturday.

Zaeef is likely to face questions about the possible whereabouts of Omar, who appeared to have escaped from anti-Taliban troops in the central Afghan mountains. Foreign ministry spokesman Omar Samad said it was highly likely Omar escaped from the area near the town of Baghran, possibly on a motorbike.

"We believe with all the publicity that has been given to his (Omar's) stay in Baghran in the past few days that it is inconceivable he would stay there," Samad said.

Gen. Tommy Franks had said Friday that there were "indications" Omar was in the area, and Samad said on Saturday that some Taliban in the area had surrendered, although he did not provide any numbers.

Al-Libi was one of 25 prisoners arriving in Afghanistan and handed over by Pakistan on Saturday. Al-Libi will eventually "be rotated out of here," according to Marine Lt. James Jarvis, with one possible destination being Guantanomo, the U.S. military base in Cuba.

Pakistan said Zaeef was deported to Afghanistan after the U.N. High Commissioner for Refugees turned down his application for refugee status.

Of the two, Al-Libi is considered by experts to be more likely to have information useful to the anti-terror effort. As well as being in charge of training terrorists, al-Libi was close to Abu Zubaydah, another aide to bin Laden involved in planning attacks.

"If Al Qaeda has plans for carrying out future terrorist attacks, this man would be involved in that, since he was the trainer," Beddington said.

Zaeef, on the other hand, was an ambassador for the Taliban — and the Taliban is all but gone.

Zaeef could help U.S. officials determine who to trust in Pakistan's intelligence agency, Beddington said. Pakistani intelligence officials had supported the Taliban as the militia took over Afghanistan, although President Pervez Musharraf removed many Taliban supporters from Pakistan's spy agency after the Sept. 11 attacks.

It is not clear, however, that any information will be gained from either man. High-ranking members of terrorist and hardline religious groups are more likely to be fanatically devoted to their cause, and accordingly, are more likely to resist questioning.

"Many of these people that we're taking control of are very, very dangerous people. They are hardened criminals," Pentagon spokeswoman Victoria Clarke said Saturday. "They're very resilient and they are very desperate."

The Associated Press contributed to this report.