The announcement brought immediate condemnation from France which termed Iran's plans a "provocation", and accused Tehran of repeated violations of international law.
"We will transfer the 20 percent enrichment from Natanz to the Fordo site this year, under the supervision of the (International Atomic Energy) Agency," Iran's atomic chief Fereydoon Abbasi Davani was quoted as saying by state television's website.
"We will also triple the (production) capacity. The 20 percent enrichment will not be stopped at Natanz until the production level is three times higher than its current rate," he said.
All of Iran's uranium enrichment activities are currently undertaken in the central city of Natanz. Fordo is located near the holy Shiite city of Qom, about 150 kilometres (94 miles) southwest of Tehran.
Revelations in 2009 about the construction of the Fordo plant infuriated the West and prompted the United Nations to strengthen sanctions against Tehran.
Iran informed the UN nuclear watchdog in February that the Fordo plant was prepared to host centrifuges -- machines which enrich uranium at supersonic speed -- and that it would become operational in the summer.
In April, Abbasi Davani said that Iran would continue to enrich uranium to 20 percent purity to fuel "four to five (research) reactors" which he said Iran plans to build in the near future.