Iran says it has taken further steps in developing its nuclear programme.
Iran produced its first enriched uranium in February
A report carried by the Iranian student news agency, Isna, says it has installed a second centrifuge cascade for uranium enrichment.
The report says Iranian scientists intend to start injecting uranium gas into it within days.
The UN Security Council set a deadline at the end of August for Iran to stop enriching uranium, threatening sanctions if it did not.
Iran rejects western criticism of its nuclear programme and maintains that it is enriching uranium only to generate electricity.
BBC Tehran correspondent Frances Harrison says that while Iran's enrichment activity is still at an early stage, the latest move will be seen as an act of defiance to the United States and its allies.
Iran first produced a small quantity of enriched uranium in February. Scientists were running just one cascade then, made up of 168 centrifuges, the machines that spin uranium gas to enrich it.
Now it has emerged that Iran has doubled its capacity by installing a second cascade two weeks ago.
Some reports had suggested Iranian scientists were experiencing technical difficulties. Others said they were going slow, awaiting the outcome of political talks that have now stalled.
Iran had said earlier that it planned to install three thousand centrifuges at its site in Natanz by the end of this year.
To produce industrial-scale nuclear fuel, tens of thousands of centrifuges would be needed, our correspondent says.