Iran has announced two key nuclear-related projects that expand its ability to extract and process uranium, which can be enriched for reactor fuel but also for atomic weapons.
The development came just days after another round of talks with world powers seeking to limit Tehran's atomic programme ended in a stalemate.
Iran already has uranium mines and the ability to turn the raw ore into a material called yellowcake, which is the first step in the enrichment chain. But the new facilities - the country's largest uranium mine and processing facility - give Tehran more self-sufficiency over the raw materials and underscore Iran's drive to expand its nuclear capacities even as world powers press for concessions.
Iran and the six-nation group - the five permanent UN Security Council members plus Germany - remain at stalemate after the latest round of talks last week over efforts to rein in the nuclear programme. US Secretary of State John Kerry has said the "door was still open" for a negotiated pact with Iran, but urged its leaders to take the first steps to address international concerns that they could seek nuclear weapons.
Iran says it only wants nuclear reactors for electricity and medical applications. Iranian authorities have demanded that world powers acknowledge the country's right to enrich uranium and ease sanctions.
"President Obama could not be more clear: Iran cannot have and will not have a nuclear weapon," Mr Kerry said following talks in Jerusalem with Israeli prime minister Benjamin Netanyahu, who has warned Isreal could consider attacks on Iranian nuclear sites.
"We are open to negotiation," Mr Kerry added. "But it is not open-ended, endless negotiation. It cannot be used as an excuse for other effort to try to break out with respect to a nuclear weapon."
The announcement of the new uranium sites suggests Iran intends to keep pledges to expand its nuclear capabilities in defiance of sanctions and other diplomatic pressures.
President Mahmoud Ahmadinejad ordered the start of symbolic start of operations through a video conference for Iran's National Day of Nuclear Technology, which marks the anniversary of the first time Iran enriched uranium in 2006.
State TV simultaneously showed ceremonies at Iran's biggest uranium mine at Saghand and a uranium ore concentrate production plant in Ardakan, both in central Iran.