The US Senate has voted 87-1 to double the reward for the death or capture of al-Qaeda chief Osama bin Laden to $50m.
The US still does not know where Osama bin Laden is
The Senate vote comes amid warnings that al-Qaeda has rebuilt its capacity to mount attacks and is trying to insert agents into the US.
"It has been six years, and al-Qaeda is now rebuilding its terrorist training camps," said Senator Byron Dorgan.
Intelligence analysts told Congress on Wednesday that al-Qaeda had created a safe haven in remote parts of Pakistan.
A leaked draft of a new US intelligence report says al-Qaeda is at its strongest since just before the 11 September 2001 attacks on the US.
Homeland Security chief Michael Chertoff said earlier this week that he had a "gut feeling" that the US would be at greater risk of attack over the next few months.
President George W Bush has played down the anxiety, however:
"There is a perception in the coverage that al-Qaeda may be as strong today as they were prior to September 11th," he said on Thursday.
"That's simply not the case."
Bin Laden has not been heard from in more than a year, but his deputy Ayman al-Zawahiri has released a series of messages in recent weeks that have appeared on Islamist websites.
His most recent urged Pakistanis to rise up against President Pervez Musharraf in retaliation for the bloody storming of the militant Red Mosque in Islamabad.