**Iran has revealed to the UN nuclear watchdog the existence of a second uranium enrichment plant, reports say.**Tehran made the announcement in a letter to International Atomic Energy Agency (IAEA) chief Mohammed ElBaradei, sources are quoted as saying.
Iran has previously acknowledged it has one enrichment plant at Natanz, some 250km (150 miles) south of Tehran.
Iran is supposed to have stopped all enrichment under threat of sanctions from the UN Security Council.
News of the Iranian letter comes days before Iran is due to enter fresh talks over its controversial nuclear programme.
Diplomats close to the IAEA said Mr ElBaradei received the letter from Iran earlier this week, the Associated Press and Reuters reports.
Speaking to the BBC, the IAEA would neither confirm nor deny the reports, saying only that it was taking a serious look at the information.
If confirmed, the development would encourage fears that Iran has other secret facilities that could be used to make a nuclear bomb, the BBC’s Tehran correspondent, Jon Leyne, says in London.
Iran has always insisted its nuclear programme is for peaceful means.
But the US and other Western nations fear Tehran is planning to develop an atomic weapon.