Workers have installed the last of nearly 3,000 centrifuges at the underground site called Fordo, near the holy city of Qum, inspectors from the International Atomic Energy Agency said.
The centrifuges are only operating at about half capacity, but the progress puts Iran on the brink of creating a nuclear weapon, The New York Times reported Friday.
Amid international pressure and heavy economic sanctions against Iran, White House spokesman Jay Carney said U.S. President Barack Obama is "open to considering bilateral talks with Iran" to ensure Iran meets its nuclear transparency obligations.
"The president made clear the window of opportunity here will not remain open forever, and he will not tolerate -- if we get to the point of negotiation with Iran -- endless negotiations or negotiations that serve merely as a stall tactic," Carney said.
Tommy Vietor, spokesman for the National Security Council, said the president "is determined to prevent Iran from getting a nuclear weapon and continues to believe there is time and space for diplomacy."
"We are in a position to closely observe Iran's program and detect any effort by Iran to begin production of weapons-grade uranium," Vietor added.