The United States on Monday called Iran's decision of enriching uranium to the 20 percent level at its Fordow facility as "nuclear extortion".
This has shortened the breakout time but reports by the U.N. International Atomic Energy Agency (IAEA), which polices the deal, indicate that Iran is not moving ahead with its nuclear work as fast as it could.
In remarks at a press conference on Monday, Saeed Khatibzadeh rejected the calls from USA president-elect Joe Biden's team for talks on Iran's missile program.
Iran started violating the accord in 2019 in response to Mr Trump's withdrawal from the pact in 2018 and the reimposition of United States sanctions that had been lifted under the deal.
"The process of gas injection to centrifuges has started a few hours ago and the first product of uranium hexafluoride (UF6) gas will be available in a few hours", government spokesman Ali Rabeie said.
Foreign Minister Javad Zarif tweeted that "we resumed 20 per cent enrichment as legislated by our parliament", adding that the IAEA had been "duly notified".
"Our measures are fully reversible upon FULL compliance by ALL", he wrote.
As for Iran, it has expressed interest in once again complying with the agreement if the USA returns to the deal.
The news was met with criticism from others in the worldwide community with Israeli Prime Minister Benjamin Netanyahu leading the criticism.
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Iran maintains that it has never sought nuclear weapons and never would.
The European Union said Iran's enrichment programme would be a "considerable departure" from the deal.
The announcement of enrichment at Fordo came as fears rose that Tehran had seized the MT Hankuk Chemi.
The government is required to suspend the conditions of the JCPoA on regulatory access beyond the Additional Protocol within two months after the adoption of the law based on the articles 36 and 37 of the nuclear deal. Iran has recently been enriching up to 4.5%, higher than the 3.67% allowed by the deal, and said it plans to enrich up to the 20% it achieved before the deal.
It came after its parliament passed a bill, later approved by a constitutional watchdog, aimed at increasing enrichment to pressure Europe into providing sanctions relief.
A handout picture released by Iran on November 6, 2019, shows the interior of the Fordow nuclear facility in Qom, in the north of the country.
Before the bill became law, Mr Rouhani slammed it as "detrimental to the course of diplomatic activities".