(We want) a large number of people to begin crawling through those tunnels and caves looking for the bad folks

US Defense Secretary Donald Rumsfeld

The broadcasts and leaflets also name 21 other members of Bin Laden's al-Qaeda network believed to be in Afghanistan.

US Defense Secretary Donald Rumsfeld said he hoped the reward would offer another incentive for the Afghan people to turn over the men who are the targets of the US attacks.

"Our hope is that the dual incentive of helping to free that country from a very repressive regime and to get the foreigners and the al-Qaeda out of there, coupled with substantial monetary rewards, will incentivise... a large number of people to begin crawling through those tunnels and caves looking for the bad folks," Mr Rumsfeld said.

Reward boosted

Secretary of State Colin Powell said he was boosting the reward from $5m to $25m.

Rumsfeld: The reward presents another incentive

"I have the authority, which I will use, to authorize an award of up to $25m for the capture of Osama bin Laden," Mr Powell told reporters.

"The legal paperwork is being accomplished but that will be our position," he said.

Congress approved a $5m reward last month, and despite earlier announcements by other officials, the amount was not changed until Tuesday.

Mr Rumsfeld said the amount had already been raised.