WASHINGTON — A senior U.S. military officer expressed surprise Wednesday at the staying power of Afghanistan's Taliban, then accused the group of planning to poison humanitarian food supplies entering the country.

Rear Adm. John Shufflebeem AP/Heesoon Yim

``They are proven to be tough warriors,'' said Rear Adm. John Stufflebeem, deputy director of operations for the Joint Chiefs of Staff. ``I am a bit surprised at how doggedly they're hanging onto power.''

On the 18th day of U.S. bombing, Stufflebeem gave no indication that it would slacken soon. Secretary of State Colin Powell said he hoped the U.S. military effort in Afghanistan could be concluded before long, but he said it might extend into the Islamic holy month of Ramadan, which begins in mid-November.

U.S. warplanes kept up heavy day-and-night pounding on the outskirts of Kabul, the capital.

At a Pentagon news conference, Stufflebeem announced what he said was a warning to the people of Afghanistan that U.S. intelligence sources indicate the Taliban might poison relief supplies and blame it on the United States.

``We are confident in the information that we have that they may intend to poison one or more types of food sources and blame it on the Americans,'' Stufflebeem said. ``We are releasing this information preemptively so that (Afghans) will know if the food comes from Americans, it will not be tainted.''

Stufflebeem gave no specific information on how the alleged poisoning might be done. Another official, speaking on condition of anonymity, said the information came from multiple intelligence sources.

In northern Afghanistan near the crossroads city of Mazar-e-Shariff, opposition forces on Wednesday claimed to have killed 35 Taliban troops and captured 140 others. They claimed that about 20 U.S. troops were in the area directing U.S. air strikes in support of the opposition forces.

Asked whether opposition forces fighting the Taliban in that area were providing targeting information to U.S. officials, Stufflebeem only said, ``We are helping him and his troops and he is helping us in our effort.''

Stufflebeem said the U.S. government would use all possible means of alerting Afghans to the possibility of poisoned food supplies, apparently including leaflet drops and airborne radio broadcasts.

He provided no specifics on the kinds of food supplies that might be affected, although he noted that the Taliban are reported to have taken over some Red Cross warehouses and might be collecting food ration packages dropped by the hundreds of thousands into Afghanistan by U.S. cargo planes in recent weeks.

That the Pentagon would raise such an issue underscores the unusual nature of this conflict, which was set in motion by the Sept. 11 terrorist attacks on the United States. U.S. officials have said from the start that this anti-terror campaign would be fought on many fronts — military, diplomatic, financial and law enforcement. It also is becoming a battle for world opinion — especially the Muslim world — as the Taliban attempt to highlight civilian casualties caused by U.S. bombing mistakes.

In an attempt to counter the bad publicity over civilian casualties, the Pentagon on Wednesday provided a briefing for reporters on techniques used by the Taliban to fight the propaganda war. The briefer, who spoke under ground rules which did not permit use of his name or job title, offered examples.

He cited an Oct. 8 U.S. aerial attack on military vehicles and radar at a Taliban base near the western city of Herat. A U.S. aerial photograph of the base, displayed at the Pentagon briefing, showed what the briefer identified as a Taliban helicopter parked just yards from the base's mosque.

The briefer said that because a helicopter would normally be parked on the base's airfield, its placement next to the mosque indicated the Taliban had one of two intentions: either that it would be bombed, causing collateral damage to the mosque and offering fuel for moral outrage against the United States, or that U.S. pilots would spare the helicopter because of its proximity to the mosque. As it turned out, the helicopter was bombed and the mosque escaped unharmed, the briefer said.