Iran is still five years away from developing a nuclear weapons capability, a London-based think tank said today.
"We estimate, if everything goes right, if they throw all their effort into solving their problems, they might be able to produce enough weapons-grade uranium for a single nuclear weapon within five years," Gary Samore, editor of a new report, told BBC radio.
But Mr Samore, of the International Institute for Strategic Studies (IISS), added that it was more likely Iran would try to accumulate production capability over a longer period - 10 or 15 years - before deciding whether to acquire weapons.
The IISS's assessment of Iran's weapons programme comes just two weeks before the UN atomic watchdog is due to discuss whether to send the Islamic state to the Security Council, a move that could prompt sanctions.
The United States and European Union suspect Iran wants to use a civilian nuclear programme as cover for arms development, a charge Tehran denies.
Last month, Iran restarted uranium reprocessing work, bringing two years of talks with the EU trio of Britain, France and Germany to the brink of collapse.
The IISS report said it was unlikely Tehran had significant stocks of undeclared nuclear weapons-usable materials, essential for acquiring nuclear arms.
The IISS also warned the consequences for international non-proliferation and regional security could be severe if Iran were to acquire a nuclear arms option or weapons.
"At worst, it could lead to a long-term erosion of the Non-Proliferation Treaty, as additional countries sought to hedge their bets by acquiring latent nuclear weapons capability under the guise of dual use fuel cycle programmes," it said.
It said Iran's Arab neighbours may react by pursuing nuclear weapons, although technical and political constraints could inhibit the emergence of additional nuclear-armed states in the region for many years.