President Bush has arrived in Slovakia for Thursday's summit with Russian President Vladimir Putin.
He flew in from Germany, where he met with Chancellor Gerhard Schroeder.
Following talks in Mainz, Mr. Bush said it is vital that Iran not develop nuclear weapons.
The German leader echoed the president's views and downplayed differences between the two countries over how to convince Iran to give up its nuclear plans.
At a roundtable discussion with young business leaders, Mr. Bush again stressed the importance of building democracy. He said he will raise Western concerns over Russia's backing away from democratic reforms during the summit with Mr Putin.
Germany was the second stop of the president's European tour aimed at mending transatlantic ties strained by the war in Iraq.
Mr. Bush said the United States has good relations with Germany despite disagreements over Iraq.
The president wound up his German visit by meeting with U.S. troops in Wiesbaden to thank them for their service.