This was stated at a briefing following the results of the seventh round of negotiations on the restoration of the atomic deal, said a senior representative of the US State Department.
According to a spokesman for the department, in the midst of negotiations, it became known about Tehran's plans to double the capacity for 20% enrichment of uranium at the plant in Fordow.
He called the attempts to force the nuclear program provocative.
“I think they think they can accumulate large reserves of enriched uranium and build more centrifuges and thus get more concessions from us and give less ourselves.
Such a negotiation tactic will not work, "RIA Novosti quotes an official of the US State Department.
He stressed that continued dialogue and hopes for a diplomatic solution to the problem do not mean that Washington is unable to increase pressure on Tehran.
Iranian Deputy Foreign Minister Ali Bagheri said earlier that the United States approved Tehran's proposals on the American side providing guarantees for a nuclear deal and the need to create a verification mechanism to lift the sanctions.
Tehran remains optimistic about the future of the talks, he said.