VIENNA: A think tank that often briefs Congress and other branches of the U.S. government on Iran's nuclear program says Tehran could produce enough weapons-grade uranium to arm a nuclear warhead within two to four months.

But the Institute for Science and International Security says it would need "many additional months" to make a prototype bomb for underground testing and even longer to make a missile warhead.

The ISIS report was made available to The Associated Press ahead of publication Monday.

Iran denies any interest in nuclear weapons saying its atomic activities are purely for generating power and scientific and medical uses.

Israeli Prime Minister Benjamin Netanyahu last month told the U.N. General Assembly that the world has until next summer to stop Iran before it can build a nuclear bomb.