Iran is to start building its third uranium enrichment plant in early 2011, a top official said, defying world powers which have slapped new sanctions on Tehran for pursuing the sensitive nuclear work. Iran's atomic chief Ali Akbar Salehi, cited on state television late on Sunday, said the search for sites for 10 new enrichment facilities "is in its final stages. "The construction of one of these will begin by the end of the (current Iranian) year (to March 2011) or the start of next year, inshallah (God willing)." Iran is already enriching uranium at its main plant in the central city of Natanz and is building a second enrichment facility inside a mountain at Fordo, southwest of Tehran. The country's hardline President, Mr Mahmoud Ahmadinejad, announced the planned construction of 10 new enrichment plants late in 2009 after Tehran was censured by the UN atomic watchdog over building the Fordo facility. Salehi, who is also one of 12 vice presidents of Iran, has previously said that any new uranium plants the Islamic republic builds would be located at locations which cannot be targeted by air strikes. He did not specify where the third plant would be located. Iran's arch-foes the United States and Israel have never ruled out military strikes against Tehran to halt its nuclear programme which they suspect is aimed at making weapons. Tehran denies the charge, saying its atomic programme has purely peaceful goals. Iran's uranium enrichment programme is at the heart of its nuclear controversy and the key reason for which a fourth round of UN sanctions was imposed on the Islamic republic on June 9. Enriched uranium can be used as fuel to power nuclear reactors as well as to make the fissile core of an atom bomb.