Updated

Infantry from the Army's 10th Mountain Division have crossed from Uzbekistan into northern Afghanistan to serve as a quick-reaction force in case of renewed Taliban resistance around the city of Mazar-e-Sharif, officials said Wednesday.

The force is comprised of no more than two dozen soldiers, the officials said, speaking on condition of anonymity. One official said the numbers might be increased.

The 10th Mountain has had about 1,000 of its soldiers providing security at an air base across the border in southern Uzbekistan for several weeks, the officials said.

The rapid-reaction force apparently was not in the area when Taliban prisoners staged a bloody prison revolt Sunday. The CIA confirmed Wednesday that one of its officers, Johnny "Mike" Spann of Winfield, Ala., was killed in the riot. He was the first American known to be killed in Afghanistan since U.S. bombing began Oct. 7.

U.S. military personnel also are surveying airfields near Mazar-e-Sharif and Bagram, north of the Afghan capital, in anticipation of using them to expand the delivery of humanitarian relief supplies, officials said.

Bagram's airfield might eventually be used to launch combat operations, they said, although it was not clear whether that would be by strike aircraft like Air Force F-15s or by ground troops.

Several hundred Army and Air Force special operations forces have been inside Afghanistan for weeks, working in small teams linked with opposition forces in northern and southern parts of the country.

The only other U.S. ground troops known to be in Afghanistan are Marines setting up a base near the southern city of Kandahar.

More Marines and equipment arrived at the base Wednesday, bringing the number to between 750 and 800, Pentagon spokeswoman Victoria Clarke said. The Pentagon has said that number may increase to about 1,100 Marines, whose purpose is to deny southern escape routes for Taliban and Al Qaeda fighters.

The Marines are the only substantial U.S. ground force in Afghanistan, although the Pentagon has not ruled out eventually putting more Army troops there if the current approach to rooting out Al Qaeda and Taliban leadership fails. For now the Pentagon is content to seek intelligence from local Afghans on the enemy's whereabouts and to bomb the caves, tunnels and other facilities in which they might be hiding.

Defense Secretary Donald H. Rumsfeld alluded to the possibility of more ground forces Tuesday when he visited the Tampa, Fla., headquarters of U.S. Central Command, which is managing the war effort. "Our efforts, of course, will be shifting from cities at some point to hunting down and rooting out terrorists where they hide," he said. "This is difficult work. It's dangerous work."

Pentagon officials, meanwhile, said leaflets dropped by American planes over Afghanistan are helping persuade some Taliban troops to give up their fight.

"We're happy about that," Rear Adm. John Stufflebeem told a Pentagon news conference.

Stufflebeem said planes continue to drop leaflets with a number of messages, including those giving information on humanitarian aid, wanted posters on Taliban and Al Qaeda leaders and some to prompt defections in the few remaining parts of the country where fighters are still resisting opposition forces.

"We are starting to see some success from those," Stufflebeem said. "In having interviews with those who are detained, there is information that is coming forward that they are having a positive effect."

The Pentagon also reported that U.S. airstrikes damaged a compound southeast of Kandahar believed used by senior Taliban or Al Qaeda figures but it was unclear whether any were killed.

"They had a confluence of intelligence which led us to believe there was senior leadership in the building," said Clarke.

"We do not have names, we don't have a sense of exactly who was in there. We do not have any sense that Omar was there," she said referring to Taliban head Mullah Mohammed Omar.

Stufflebeem said about 10 bombs dropped from an Air Force B-1B bomber struck the compound. At the Pentagon news conference he showed video of the strike as recorded by an Air Force F-16 accompanying the bomber.