President Bush renewed his pledge Tuesday to work with allies to bring justice to terrorists, but even as he spoke, a new terrorist threat was surfacing in France.
Speaking to reporters after a meeting with Dutch Prime Minister Jan Peter Balkenende (search), Bush said "the free world" must continue to be "strong and resolute and determined" in battling terrorism.
Terrorists will "never shake the will of the United States. We understand the stakes," Bush said.
The president also urged allies to keep troops in Iraq, saying the coalition needs to remain united.
"It's essential that we remain side-by-side with the Iraqi people as they begin the process of self-government," he said.
Balkenende is another leader under pressure to withdraw troops from the mission in Iraq, which many Europeans don't see as part of the war on terror.
On Saturday, two days after a devastating terror attack in Madrid that killed 201 people, Spanish citizens rode a wave of anger and ousted the Popular Party of Jose Maria Aznar (search), a Bush ally, and elected anti-war Socialist Jose Luis Rodriguez Zapatero (search) as president.
"Their support for us under Zapatero will be conditional where as under Aznar it was almost unconditional," said former Ambassador Richard Gardner. "Don't forget Aznar had 90 percent of the people who were against the war."
Investigators believe Spain's support of the United States in Iraq may be the reason for Thursday's bombing. Zapatero has said that he will withdraw Spain's 1,300 troops from Iraq by June 30 unless the mission there is put under U.N. auspices.
Despite the move, Zapatero said that he would like to keep cordial relations with the United States, but with his decision for a pullout and the apparent rejection by Spanish voters of U.S. policy toward Iraq, Bush sought to encourage other allies not to change course.
"I would remind the Dutch citizens that Al Qaeda (search) has an interest in Iraq for a reason, and that interest is they realize this is a front in the war on terror and they fear the spread of freedom and democracy in places like the greater Middle East."
Bush reminded Dutch citizens that the people of Iraq do not want the withdrawal of troops that are protecting their freedom. For his part, Balkenende said it was important that the international community stands "shoulder to shoulder and shows its solidarity to fight against these terrible attacks. We share that same goal."
Bush added that it is up to Balkenende to decide whether to keep his troops in Iraq, but said, "We both agree that a free Iraq is essential to a peaceful world. We both understand the stakes. We both know that Al Qaeda is interested in fighting us in Iraq."
White House aides say the bombings in Spain prove terrorists are indiscriminate and can't be reasoned with. U.S. officials say they might seek a U.N. resolution to persuade Zapatero to keep his troops in Iraq, but they barely contained their disappointment over the threat to withdraw them.
"It is the wrong message to let terrorists think that they can influence policy, that they can influence elections," said White House Press Secretary Scott McClellan.
"They have not only killed in Spain, they've killed in the United States, they've killed in Turkey, they've killed in Saudi Arabia. They kill wherever they can," Bush said.
As the president spoke on Tuesday, the French newspaper Le Parisien and other news outlets received a fax from an Islamic group threatening terrorist attacks in retaliation over French plans to ban Islamic headscarves and other religious apparel in schools. The group identified itself as The Servants of Allah, the Powerful and Wise.
French government officials said they were taking the threat seriously, but urged people not to panic. In response to the threat, France's president once again seemed out of sync with the United States, calling for a European plan to fight terrorism, but with a strategy that emphasized conciliation.
"Let's be realistic: Together, we must also put an end to the conflict that breeds peoples' anger and frustration," said French President Jacques Chirac.
U.S. officials say the war on terror is scoring victories, and the man leading the troops in Iraq said the United States will get the job done, with or without Spanish troops.
"Those are national decisions that have to be made, and as a commander on the ground, once a nation makes those kind of decisions, we'll adapt," said Gen. Ricardo Sanchez.
Secretary of Defense Donald H. Rumsfeld acknowledged Tuesday that the decision by Spain's new leader to pull troops from Iraq is a setback for the United States, but told the British Broadcasting Corporation that the job will get done in any case.
So far, no other countries have said they will pull out their troops. The Bush administration hopes to keep it that way, but acknowledges that U.S. allies could pay a price for their allegiance. An FBI official visiting Australia on Tuesday warned the nation's leaders that it should brace for a terrorist attack because of its close ties to Washington.
"Any country that allies itself with the United States, unfortunately, is a target," John Pistole, the FBI's executive assistant director for counterterrorism, told Sydney's 2UE radio station.
Bush and his aides, however, continue to stress that it is in the interest of all nations to remain allied with Washington.
"My guess is, you'll find other countries reacting just the opposite. You'll find countries stepping forward and saying, 'Well, if that's what that country's going to do, we'll do just the opposite. We'll add some troops,'" Rumsfeld said. "And, we'll see what happens."
Fox News' Wendell Goler and Caroline Shively and the Associated Press contributed to this report.