But the Western powers believe the Islamic state is seeking a capability to build atomic weapons.

Obama said the US, Britain and France Thursday presented 'detailed evidence' to the Vienna-based UN nuclear watchdog, IAEA, showing Iran has been building a 'covert uranium enrichment facility' near the southern city of Qom.

Under an agreement with the IAEA and UN Security Council resolutions, Iran is required to inform the nuclear monitoring agency of all of its atomic activities.

It was previously believed that Iran's only nuclear enrichment facility was located at Natanz, where Iran says it is only seeking to enrich uranium at lower concentrations for nuclear reactors.

But the US and its allies fear Iran could intensify the process to enrich uranium at much higher levels adequate for building weapons.

'Iran must abandon any military ambitions for its nuclear programme,' Brown said.

The UN Security Council in recent years has adopted three resolutions placing limited sanctions on Iranian for its refusal to suspend uranium enrichment.

Obama has sought to reach out to Iran to begin negotiations on the contentious issue that has been on the top of the international agenda for years.

Iran has maintained that like other nations it has a right to nuclear energy and firmly rejects demands to stop enriching uranium.

The international effort to rein in Iran's nuclear work has been spearheaded by Britain, China, France, Russia and the US - the five permanent members of the Security Council - and Germany.