"We are taking all the necessary measures to defend our country," government spokesman Abdullah Ramezanzadeh told reporters.
"Our objectives are purely defensive," he added, saying the "measures taken are clear as crystal and do not violate any of our international accords."
"We are obliged to defend our national interests when there are evil powers in the world," he said, without elaborating.
Ramezanzadeh was responding to a statement from the Iraq-based National Council of Resistance of Iran (NCRI) on October 16 saying Tehran was testing missiles with a 2,000-kilometer (1,240-mile) range, capable of delivering chemical and biological warheads to targets as far as Europe and North Africa.
The NCRI's Soona Samsami also said that Iran was developing a Shahab-5 missile with a 5,000-kilometer (3,000-mile) range.
The NCRI is the political wing of the People's Mujahedin, the main armed opposition group, based in Iraq. It is on Washington's list of international terrorist groups.