"As long as the threat from Iran persists, we will go forward with a missile defence system that is cost-effective and proven," he told a crowd of about 20,000 gathered in Hradcany Square, next to Prague Castle.
"Iran's nuclear and ballistic missile activity poses a real threat, not just to the United States, but to Iran's neighbours and our allies."
He hailed the "courageous" Czech Republic and Poland for "agreeing to host a defence against these missiles". Russia is strongly opposed to radar stations for a missile defence shield being established in countries that it still regarded as within its sphere of influence.
But Mr Obama also spoke of the potential for a rapprochement with Iran that would remove the need for such a system.
"If the Iranian threat is eliminated, we will have a stronger basis for security, and the driving force for missile defence construction in Europe will be removed."
It sounds like Obama's support for missile defense is still too squishy. If his commitment to missile defense is as serious as his commitment to free-market capitalism, we're in trouble.
33 Minutes: Protecting America in the New Missile Age
Newt: I would've disabled the missile
Reacting to President Barack Obama’s speech in Prague, Gingrich called the plan for a Global Summit on Nuclear Security a “wonderful fantasy idea,” saying Russia and other nations can’t be trusted.
Here's the bottom line. Somewhere on this globe some nation or some organization is going to be more powerful than all of the others. Who is going to carry the big stick? Right now the choices seem to be between the United States, Russia, China or the United Nations. Go ahead ... chose one.
Are you even at the "e-mail" stage of anger?
Tea Party in San Antonio
Don't Mess With Texas!