Iran has officially dropped some of its commitments to the 2015 nuclear deal in line with President Hassan Rouhani's announcement last week.
The country stopped some commitments, including limits on its uranium enrichment programme, after an order from its National Security Council, the country's atomic energy agency told the Isna news agency.
An official from the agency said Iran now had no limits on its production of enriched uranium and heavy water.
Under the nuclear deal, Iran set limits of 300 kilograms on the amount of uranium it can produce, and 130 tonnes of heavy water.
The deal limits the enrichment of uranium to 3.67 per cent, far below the 90 per cent required for weapons-grade material.
Before the deal, Iran enriched uranium to 20 per cent, a level the country’s supreme leader Ayatollah Ali Khamenei said it could easily reach.
"Achieving 20 per cent enrichment is the most difficult part," Mr Khamenei told the Iran newspaper's Wednesday edition. "The next steps are easier than this step."
Iranian officials have said they could reach 20 per cent enrichment within four days.
Although the country says its nuclear programme is for peaceful purposes, scientists say the time required to reach the 90 per cent threshold is halved once 20 per cent enrichment is reached.
Last week, the country notified the other signatories of the deal – China, France, Germany, Russia, the UK and the EU – of its decision to pull out of some commitments, after the US withdrew and reimposed sanctions.
The US imposed further sanctions on Iran after its announcement, this time on their metals industry.
The US moved USS Abraham Lincoln, an aircraft carrier, plus B-52 bombers to the Gulf last week. Iran called them a target, not a threat.
Mr Khamenei also said talks with the US would be "poison" but that the battle of words would not spill into war.
"Neither we nor them is seeking war," he said. "They know that it is not to their benefit."
On Wednesday Iran's Minister of Defence, Amir Hatami, said the country would "defeat the American-Zionist front", the Irna news agency reported.
Iran gave European countries 60 days to salvage the nuclear deal, warning that it would start enriching uranium at a higher level.
Russia and China urged Iran to maintain its commitments as a part of the deal, and European countries have urged compliance, saying they would not accept ultimatums.
The nuclear deal, or Joint Comprehensive Plan of Action, was signed in 2015, lifting international sanctions in exchange for Iran curtailing its nuclear programme.