The U.S. military took unprecedented precautions Thursday as it began to fly hundreds of extremely dangerous Taliban and Al Qaeda prisoners from Afghanistan to a special prison in Guantanamo, Cuba.

The prisoners, who were being held in Kandahar, Afghanistan, have been hooded and chained and may be drugged for the approximately 20-hour flight to make them less of a threat.

There were reports that the men were flown out in paired sets of 10 each and had their beards shaved off for reasons of hygiene.

Small arms fire erupted from the northern edge of the Kandahar base as the plane took off, and the Marines responded with heavy fire, Marine Lt. James Jarvis said. A sustained firefight lasted at least a half-hour, witnesses said. Military helicopters were circling the area, looking for the source of the incoming fire, Jarvis said.

"We have encountered enemy fire and we are engaging them," Jarvis said. He said he knew of no reports of injuries or deaths at the base.

Military officials had to shuttle hundreds of sometimes fanatical prisoners from various locations in Afghanistan to the Marines' main jail at the airport outside Kandahar. Others were moved from the Navy's USS Bataan in the Arabian Sea.

"These people vowed to win their way into paradise by murdering anybody in American uniform, or for that matter, any civilians," said spokesman Steve Lucas at the U.S. Southern Command, the Miami-based command that is helping coordinate the move, in reference to the terrorists' radical Islamic beliefs. "The level of threat is probably unique."

As they fly to the Western Hemisphere, the prisoners will be chained to their seats and possibly sedated, forced to use urinals and fed by their guards, newspaper and television reports said.

Pentagon spokeswoman Victoria Clarke wouldn't comment on the reports, except to say detainees were being treated in accordance with the Geneva Convention rules on prisoners.

Defense Secretary Donald Rumsfeld said at a Thursday afternoon press conference that American military officials would do whatever they could to make sure the prisoners were taken to Cuba safely with "appropriate restraints." 

"They are authorized to use whatever restraints are needed," he said. "They have reviewed the Mazar-i-Sharif uprising (and) reviewed Pakistan army problems as they tried to detain them."

He noted that other groups of Al Qaeda and Taliban prisoners had killed their guards in at least two instances in the war.

"They're fully aware that these are dangerous individuals," Rumsfeld said of American troops. "There are among these prisoners people perfectly willing to kill themselves and others."

Clarke told a Thursday press briefing that she was trying to determine what details of the transfer would be released, saying officials would not be talking about schedules or other things that would breach security, but would simply announce when the detainees had reached the U.S. military base in Guantanamo.

Preliminary plans were to take the prisoners from Kandahar on C-17s to a base in Europe, where they could be transferred to C-140 cargo planes for the remainder of the trip to Cuba.

Their new home will be newly constructed jail cells in Guantanamo built after a prison uprising at an Afghanistan prison that led to the murder of a CIA officer. It's going to be an unprecedented security challenge for the Guantanamo base, which is also fenced in by the less-than-friendly Cuban military.

"This thing is being done ... with the most expertise that we can bring to bear on it," Lucas said. "These suicidally murderous people have compatriots at large. We don't want to provide them any information that could make a big terrorist splash."

In addition to the uprising that killed American CIA officer Johnny "Mike" Spann, escaping prisoners also killed Pakistani guards in an attempt to escape into Pakistan, prompting even tighter security by the U.S. military.

"Nothing like this to my knowledge has been done before (considering) the level of threat and probably the size and distance too," Lucas said of the transfer. "I'm not sure that anyone has every handled detainees of this type and transferred them 20 hours or whatever it is — around the world."

The regrouping of prisoners overnight Wednesday brought the number in Kandahar to 351, said Lt. Col. Martin Compton at the U.S. Central Command's war command center in Tampa, Fla. A total of 371 are in U.S. custody, with 19 remaining in Bagram, one on the Bataan and none in the northern city of Mazar-e-Sharif, he said.

Those prisoners in U.S. custody have been selected from among thousands captured by Afghan fighters as they took one city after another from the former Taliban rulers who had been harboring Usama bin Laden and his Al Qaeda terrorists.

The Associated Press contributed to this report.