In a keynote speech in Poland, Bush also said commitments by new Palestinian Prime Minister Mahmoud Abbas to oppose attacks on Israelis were a "hopeful sign" for peace in the Middle East.

"The United States is committed to a strong Atlantic alliance, to ensure our security, to advance human freedom and to keep peace in the world," Bush said in Krakow.

"This is no time to stir up divisions in a great alliance," he said, calling for global cooperation against "terrorism."

Bush made Poland the first stop on his week-long trip to Europe and the Middle East, thanking Poles for their support in the war to overthrow Iraq's Saddam Hussein.

He will seek to build bridges with France and Germany, dismissed by Defense Secretary Donald Rumsfeld as "old Europe," and with Russia at talks in St Petersburg later on Saturday, followed by a Group of Eight summit in the French town of Evian.

"As the Atlantic alliance has expanded it has also been tested... Each nation has faced difficult decisions about the use of military force to keep the peace. We have seen unity and common purpose. We have also seen debate: some of it healthy, some it divisive," Bush added in Krakow.

Bush, trying to end violence by meeting the Israeli and Palestinian prime ministers in Jordan next week, said he saw a hopeful sign that his vision on the Middle East can come true.

"Today in the Middle East the emergence of a new Palestinian leadership, which has condemned terror, is a hopeful sign that the parties can agree to two states, Israel and Palestine, living side by side in peace and security," he said.

"The work ahead will require difficult decisions...For peace to prevail all leaders must fight terrorism."

"I will do all that I can to help the parties reach an agreement and then to see that that agreement is enforced."

Earlier in the day, a grim-faced Bush toured the Auschwitz-Birkenau death camps, pausing at the ruins of a Nazi crematorium to make his case to the people of Europe.

"Mankind must come together to fight such dark impulses," he said at the sprawling complex where German invaders committed genocide during World War II with assembly-line efficiency.

Meanwhile, President Bush toured the Nazi death camps of Auschwitz and Birkenau on Saturday, stating his case for standing up to "evil" dictators.

Pausing before the brick ruins of a crematorium, Bush said Hitler's gas chambers were a "reminder of the power of evil and the need for people to resist evil."

"This is also a strong reminder that the civilized world must never forget what took place on this site," he said.