U.S. military forces will do "whatever is necessary" to root out the Taliban and Al Qaeda terrorists from their cave hide-outs, Defense Secretary Donald H. Rumsfeld said Sunday. 

Rumsfeld acknowledged the difficulty of locating and penetrating cave systems, deep in the mountains of Afghanistan, that are multilayered, sophisticated and self-sustaining. 

The decision has not been made whether U.S. ground forces will be sent on a cave-by-cave manhunt. For now, the U.S.-led campaign is relying on airstrikes near Kandahar, the Taliban's last major stronghold, and in the mountains south of Jalabad in eastern Afghanistan, and hoping $25 million in reward money will provide Usama bin Laden's whereabouts. 

Anti-Taliban forces claimed U.S. bombing raids had mistakenly destroyed one of their headquarters in Afghanistan's mountainous east early Sunday, killing at least eight people. 

At U.S. Central Command headquarters in Tampa, Fla., spokesman Lt. Col. Mark Compton said the command was looking into the reports but had no immediate information about the latest attacks. 

Asked on NBC's Meet the Press whether poison gas would be pumped into the caves, Rumsfeld noted that Northern Alliance forces used flooding to force the surrender of the last Taliban holdouts in a prison fortress near Mazar-e-Sharif in the north. 

"I guess one will do whatever it is necessary to do," Rumsfeld said. "If people will not surrender then they've made their choice." 

Rumsfeld said Pentagon officials do not know exactly how many Taliban fighters remain in and around Kandahar, in the southwest, only that they number in the thousands. 

"The remaining task is a particularly dirty and unpleasant one," Rumsfeld said. "We expect that there will be casualties, we expect that there will be people captured." 

He said the main barrier to bringing in forces from other nations to assist the U.S. campaign was the opposition of Afghan anti-Taliban officials. 

"We are very anxious to have the right kind of help," he said. 

It has been difficult to convince the Northern Alliance to allow non-American troops into their areas of control, Rumsfeld said. 

The defense secretary also said it is possible that Afghan forces will be able to maintain order in their country themselves, without the help of a multinational peacekeeping force. But if such a peacekeeping mission is needed, it cannot hinder a continuing U.S. military effort that will last longer than just a few more months, Rumsfeld said. 

"We've got an awful lot to do," he said.