President Bush ratcheted up the rhetoric when he said he wanted Osama bin Laden "dead or alive" and would hunt him down remorselessly.
And he spoke of the cost America would have to pay. "Freedom has a cost and we are willing to bear that cost," he said.
Speaking to reporters during a visit to the Pentagon, Mr Bush put Afghanistan's radical Islamic Taliban government, which offers Saudi-born bin Laden its protection, on notice that it would also be held accountable for last Tuesday's attacks.
Asked if he wanted to see death for bin Laden, Mr Bush said: "I want justice. And there's an old poster out West that says, 'Wanted: Dead or Alive'." His spokesman said later he could not elaborate on the comments and there was no state bounty on bin Laden's head.
"We are going to find those evildoers, those barbaric people who attacked our country, and we're going to hold them accountable, and we're going to hold the people who house them accountable, the people who think they can provide them with safe havens will be held accountable, the people who feed them will be held accountable, and the Taliban must take my statement seriously," Mr Bush said.
The President was at the Pentagon to discuss plans to mobilise reservists to beef up domestic defences against terrorism.
Asked if a formal US ban on the use of assassination would hinder any effort to kill bin Laden, White House spokesman Mr Ari Fleischer said the prohibition "is in effect but it does not limit America's ability to act in self-defence". Asked why Washington thought it appropriate, in effect, to issue a global call for bin Laden's head, he replied: "Our nation's been attacked, and we are at war, and to win a war it is vital for the United States to engage in it.
"Our nation will defend itself, and defending itself means acts which involve the lives of others. We will defend ourselves, and the United States will act in its self-defence and that is why."
Mr Bush, who has been planning a global war on terrorism, acknowledged the likelihood of casualties, saying "there will be costs. But the military folks understand that, so does the Secretary of Defence." He said he had faith that the US economy would shake off the blow from the attacks.
"I understand it's tough right now," he said. "The transportation business is hurting. Obviously the market was correcting prior to this crisis, but the underpinning for growth is there.
"But there is a challenge ahead of us, and I'm confident that the business community will rise to the challenge," he said.
Asked about the spirit of the US military, Mr Bush said he was confident it was "ready to defend freedom at any cost". On the call-up of 35,000 reservists the President said they would play a number of roles - maintaining air defences, checking shipping in ports, helping in airlifts, military police, engineering projects and gathering intelligence.
Mr Bush continues to work to build international support for his attack on terrorism. Last night it was announced that British Prime Minister Mr Tony Blair will travel to Washington on Thursday for talks with President Bush, and then to New York. The German Foreign Minister, Mr Joschka Fischler, will also visit Washington for talks.
The Blair visit will be seen as an important show of British support for the US position.
"Mr Blair welcomes the fact that the American administration is consulting widely and building a coalition of international support for any response to last week's atrocities," a Downing Street spokeswoman said.
Mr Blair is hoping to visit the scene of the attack and will meet British people who are waiting for news on missing relatives.
