President Bush says there is 'no question' Osama bin Laden is the prime suspect behind the US terrorist attacks.
Speaking to reporters on the White House lawn, he asked the American people to be patient with their Government.
He repeated his pledge to hunt down the people responsible for the attacks.
He said: "This crusade, this war on terrorism, is going to take a while and the American people must be patient."
Mr Bush added: "This will be a long campaign, a determined campaign."
He said those who had attacked America would be destroyed.
The president added that his diplomatic efforts are proceeding well. He told reporters he's had a "very good, open conversation" with General Pervez Musharraf of Pakistan.
He added: "There is no question he wants to cooperate with the US. The responses from Pakistan, India and Saudi Arabia have been very positive, very straightforward. They know what my intentions are."
Standing beside First Lady Laura Bush, the president said: "It is time for us to win the first war of the 21st century decisively.
"The American people should know that my administration is determined to find, to get them running, and to hunt down those who did this to America."