A US man of Iranian descent has been sentenced to death by a court in Tehran for spying for the CIA.

Amir Mirzai Hekmati was "sentenced to death for co-operating with a hostile nation, membership of the CIA and trying to implicate Iran in terrorism," semi-official Fars news agency said.

The 28-year-old's US-based family say he was in Iran visiting grandparents.

The sentence comes at a time of fresh tensions between Iran and the West over Tehran's nuclear programme.

Iran's Supreme Leader Ayatollah Ali Khamenei said on Monday that further sanctions imposed by the West "will not have any impact on our nation".

"The Islamic establishment... knows firmly what it is doing and has chosen its path and will stay the course," he said in a speech broadcast on state television.

Diplomats at the Vienna-based International Atomic Energy Agency (IAEA) confirm work has begun at an underground site near the holy city of Qom to enrich uranium to near weapons-grade level.----

More on the BBC's website: http://www.bbc.co.uk/news/world-middle-east-16465820