TEHERAN - Iran has started work on a new uranium enrichment nuclear plant, a senior official said on Monday, part of a big expansion of its nuclear program which has contributed to fears in the West it aims to build a bomb.

Defying Western pressure to curb its sensitive nuclear work, Iran announced in November it planned to expand its enrichment activities by building 10 new sites. The announcement was condemned by the United States and its European allies.

"The president has confirmed the designated location of a new nuclear site and on his order the building process has begun," Mojtaba Samareh-Hashemi, a senior adviser to President Mahmoud Ahmadinejad, told the semi-official ILNA news agency.