Updated

The Pentagon, hoping to intensify pressure on the Taliban, has decided to put military aircraft at one or more airfields in the former Soviet republic of Tajikistan on Afghanistan's northern border, a senior defense official said Monday.

The decision follows an onsite assessment by U.S. military advisers of the feasibility of using as many as three Tajik airfields. The Tajik government had offered the bases for U.S. use against Afghanistan, and the decision to go ahead could mean more Air Force fighter-bombers will be sent there soon.

The U.S. defense official, who discussed the matter on condition of anonymity, said it was not yet clear how much local improvement would be needed before the airfield could be put to use. The official was not certain which airfield was chosen out of three offered: Kulyab, Khojand and Kurgan-Tyube.

The U.S. military already is using one airfield in Uzbekistan, where at least 1,000 soldiers of the U.S. Army's 10th Mountain Division are based. It also has made use of military facilities in Pakistan, although nearly all combat missions have been flown from aircraft carriers in the Arabian Sea and from a British base in the Indian Ocean. Some missions have been flown from Persian Gulf nations.

The significance of using one or more airfields in Tajikistan is twofold: It offers a chance to fly shorter attack missions in support of anti-Taliban forces, possibly offering some relief to Navy pilots who have been flying long missions from carriers, and, secondly, it offers an opportunity to expand the delivery of humanitarian relief to Afghans.

Victoria Clarke, chief spokeswoman for Defense Secretary Donald H. Rumsfeld, said Monday that the U.S. government is focusing hard on an expanded humanitarian relief effort, now that Taliban forces have lost control of the northern city of Mazar-e-Sharif and are on the run elsewhere in the country.

"There's an intensive effort under way," she said.

Thus far the delivery of food rations and other humanitarian relief has been limited to airdrops by Air Force C-17 cargo planes flying from Germany. More than 1.3 million food packets have been delivered, but the Pentagon has been eager to find more efficient means -- namely overland deliveries.

Defense officials said the situation in Kabul, the Afghan capital, was unclear. News reports from the city said the Taliban had deployed tanks at major roads leading into the capital in anticipation of an all-out assault by opposition forces supported by the United States. Security was dramatically increased, with heavily armed Taliban fighters searching vehicles at intersections.

U.S. officials said they were cautiously encouraged by opposition gains in recent days, especially by reports from Mazar-e-Sharif and other cities that opposition troops were welcomed as liberators.

The officials also said they had received reports that communications between the Al Qaeda forces of Usama bin Laden and the Taliban had been further hampered by recent U.S. bombing -- adding to the difficulty of mounting a defense against the opposition forces.

Rumsfeld said on Sunday there was friction between leaders of Al Qaeda and the Taliban, although he did not elaborate. A U.S. official on Monday said there were significant disagreements between the two groups over military tactics.