U.S. airstrikes are targeting leaders of the Al Qaeda terrorist network and the Taliban government that is harboring them in Afghanistan, Defense Secretary Donald H. Rumsfeld said Thursday.

"They represent a significant part" of the military command and control facilities that U.S. bombs and missiles are striking, he told reporters.

Rumsfeld was asked whether U.S. intelligence has determined that Usama bin Laden remains in hiding in Afghanistan.

"The probability is that he is," Rumsfeld replied, adding that even if he were captured or killed, the war on terrorism would continue because it involves other groups of terrorists in other parts of the world.

Amid conflicting reports on whether the United States has been using 5,000-pound "bunker busters" bombs in Afghanistan, Rumsfeld said those and a wide variety of other munitions were being used.

He was asked specifically about the GBU-28, a 5,000-pound bomb developed during the Gulf War in 1991 to penetrate deeply buried targets like command and control bunkers.

The full range of precision-guided munitions have been used -- "including those" -- he said.