TEHRAN, Iran — Iran said Monday it will begin building a new site to enrich uranium by March, moving ahead with a plan that defies international efforts to curb its nuclear development.

Uranium enrichment factories are used to create fuel for nuclear power plants but can also, if taken to extremes, produce the material for weapons.

The planned plant is among 10 new sites that Iran approved last year in what would be a dramatic expansion of its controversial enrichment program. The announcement on state TV said the locations for the sites have been determined but gave no details.

“Construction of a new uranium enrichment site will begin by the end of (the Iranian calendar) year (March 2011) or early next year,” Salehi said.