U.S. Defense officials said more American troops will be sent to the Tora Bora area of Afghanistan to press the search for Osama bin Laden.

Defense Secretary Donald Rumsfeld told reporters that U.S. and coalition troops will be sent to the Tora Bora area to join in the search of abandoned caves used by al-Qaida fighters.

Two top U.S. military officials said Friday that they do not know if Osama bin Laden is dead or alive. And Secretary Rumsfeld had this response to a reporter's question about whether it is possible that the most wanted man on earth could have slipped out of Afghanistan in a small plane: "In Afghanistan, most things are possible. It is a difficult environment, it has got a porous border. There are mountainous areas with valleys, the weather is uncertain. There is no question but that there have been various reports that helicopters or light aircraft might have gone in or out. We have not been able to validate it. And we do not have any specific knowledge," he said.

Mr. Rumsfeld said the cave-by-cave search in Tora Bora has produced documents and information that has been used to arrest suspected terrorists in other parts of the world and prevented terrorist activities, though he would not be specific.

Secretary Rumsfeld also said that within the past 24 hours, American planes attacked a convoy southwest of Tora Bora that U.S. officials believe was carrying leaders of either the al-Qaida network or the Taleban. "But it was a large convoy and there were a lot of people killed and a lot of vehicles damaged or destroyed, I should say," added Mr. Rumsfeld.

As part of the intensified effort to thoroughly flush out the caves in the Tora Bora area, U.S. Defense officials announced Friday that they are sending a type of bomb that uses a delayed, high-pressure explosion that will suck the air out of tunnels and caves where al-Qaida members might be hiding.