The Associated Press
He said that if that threat is removed, "The driving force for missile defense in Europe will be removed."
In his speech before cheering crowds in historic Prague, Obama said the U.S. will present Iran with "a clear choice" to cease its nuclear and ballistic missile activity or face increased isolation and a nuclear arms race in the Middle East.
"Let me be clear: Iran's nuclear and ballistic missile activity poses a real threat, not just to the United States, but to Iran's neighbors and our allies," the president said. "As long as the threat from Iran persists, we intend to go forward with a missile defense system that is cost-effective and proven."