Ali Larijani, secretary of Iran's Supreme National Security Council, was quoted by IRNA news agency as saying the initiative was the "joke of the year," and that Tehran's missiles did not have the range to reach Europe.
Russia has also criticized Washington's plans to put a radar system in the Czech Republic and interceptors in Poland.
Russian President Vladimir Putin said in a June 3 interview that if the U.S. missile-defense plan went forward, Russia could retaliate by pointing its missiles at targets in Europe.
"If a new missile-defense system will be deployed in Europe, then we need to warn you today that we will come with a response," Putin said. "We have to ensure our security, and we are not the initiator of this process."
U.S. President George W. Bush is due to arrive later today in Prague for a visit aimed at persuading the Czech Republic to accept the U.S. radar system.
Bush and Putin are due to meet at the summit of the Group of Eight (G8) industrialized economies beginning on June 6 in Germany.
(compiled from agency reports)