White House spokesman Ari Fleischer said the Defense Department was trying to confirm the incident and determine whose weapons were involved. He raised the possibility that anti-aircraft fire from the ground could be responsible.

"In a case like this, ... it's hard to say whether something was a result of anti-aircraft weaponry that was shot from the ground, or other weapons that were shot from the ground and came back down, or whether or not it was coalition efforts," Fleischer said.

A bomb crashed into a Red Cross compound at Khair Khana near Kabul, injuring a guard and setting afire two warehouses containing wheat, medicine and other supplies. Officials in Pakistan said the roofs of the warehouses were marked with Red Cross insignia.

The incident happened as President Bush prepared to visit Red Cross headquarters in Washington to encourage Americans to take part in community service efforts during the military strikes. Bush did not mention it in his remarks, and did not respond to questions shouted by reporters.

Bush said the White House had received 90,000 pieces of mail since Friday in response to his call for American children to each donate $1 toward relief efforts for Afghan children.

"In just a few short days, children all across our country have responded with remarkable generosity and deep compassion," Bush said.

Some children were chipping in much more than $1, Bush said. He noted that entire classes of students were pooling their contributions and personally congratulated Kristen Strickland of Philomont, Va., who raised $45 by feeding chickens.

He said he would ensure that each dollar raised by children in the United States would be spent on the needs of children in Afghanistan as that country's harsh winter approaches.

"The children need warm clothing. And they need food, and medicines," Bush said. "Thanks to the American children, fewer children in Afghanistan will suffer this winter."