Iran has announced that the construction of the first of 10 new uranium enrichment facilities in the country will start early next year.
Ali Akbar Salehi, the head of Iran's nuclear programme, told state television that the search for sites for the facilities "is in its final stages".
"Construction of a new uranium enrichment site will begin by the end of the [Iranian] year [March] or early next year," Salehi said on Monday.
"The new enrichment facilities will be built inside mountains."
Western powers have imposed several rounds of sanctions aimed at curbing Iran's nuclear activities amid fears that it aiming to produce nuclear weapons.
But Iran insists that its nuclear programme has only peaceful intentions.
Mahmoud Ahmadinejad, the Iranian president, originally announced plans to build the 10 new plants late last year.
"We insist that we we will have to use our rights for our own national interest," Salehi told Al Jazeera.
"We are exploring Iran now and we have seen promising places that contain [a] relatively good amount of uranium and the ability to enrich it."
Enriching uranium creates fuel for nuclear power plants but can also, if taken to higher levels (90 per cent) produce the material for an atom bomb.
Iran says it is enriching uranium to 20 per cent to produce fuel for a research reactor in Tehran.
On Monday, Ahmadinejad signed a new law which obligates his government to continue the 20 per cent uranium enrichment work.
The new law also stipulates that the government "co-operate with the IAEA (International Atomic Energy Agency) only under the framework of the Non-Proliferation Treaty's (NPT) general regulations".
It bans any co-operation that goes beyond the NPT requirements, Iran's English language Press TV said on its website, a measure likely to anger Western powers.
The United Nations Security Council in June imposed a fourth set of sanctions against Iran and the European Union and the United States have added even more extensive sanctions targeting its foreign trade.
Steve Field, the spokesman for David Cameron, the British prime minister, said Salehi's announcement was a cause for concern.
"The reports that we have seen this morning certainly do not give us any comfort that Iran is moving in the right direction," Field told reporters.
Christine Fages, a French foreign ministry spokeswoman, said the announcement "only intensifies the deep worries of the international community about the Iranian nuclear programme".
"We want Iran to respect its international obligations by suspending all its activities of uranium enrichment," she said.