The US, Britain and France united in condemnation of Iran on Friday after Tehran’s admission that it has been constructing a secret uranium enrichment facility that Washington fears could help produce a nuclear bomb.

As the world’s major powers prepare to meet Iran next week for critical talks on its nuclear programme, US President Barack Obama disclosed the existence of the plant, 160km south of Tehran.

On Saturday, Iranian media reported that the Revolutionary Guards will stage missile defence exercises starting on Sunday. The war games announcement is expected to futher heighten the nuclear dispute.

Iran has been enriching uranium at the plant in Natanz under inspection but it had never before admitted the existence of the second site to the United Nations’ nuclear watchdog, the International Atomic Energy Agency.