European countries and the US should return to the negotiating table or Iran would enrich uranium at a higher level, President Hassan Rouhani said on Wednesday.
Mr Rouhani said Iran's Arak nuclear plant would enrich uranium beyond the 3.67 per cent level to "whatever levels we need" on July 7 if other signatories did not fulfil their commitments, the IRIB news agency reported.
Before the 2015 nuclear deal, Iran had enriched uranium to 20 per cent, halfway in time to the near 90 per cent level necessary for weapons-grade material.
Uranium refined to 3.67 per cent is deemed suitable for electricity generation. The Arak nuclear plant is a heavy water facility that was modified under the 2015 deal with world powers.
An increasing stockpile and higher enrichment reduces the estimated one year Iran would need to produce enough material for a nuclear bomb, something Tehran denies it wants.
But Mr Rouhani said it would remain committed to the deal if the European and American signatories kept their side of the agreement.
He said, however, that Europe had not offered anything to ease the pain of renewed US sanctions.
On Monday, Iran breached the limit for the quantity of enriched uranium it could hold, saying the US reimposing sanctions was cause for exceeding the 300 kilogram limit.
Mr Rouhani said Iran's reduction in commitment was not intended to "strike a blow" to the deal, but to preserve it.
"Iran will gain nothing by leaving the Vienna accord," a spokeswoman for the French Foreign Ministry said.
"Putting it into question will only increase the already heightened tensions in the region."
EU countries on Tuesday called for Tehran to comply with the deal, saying their commitment to it relied on "full compliance" by Iran.
The UK, France, Germany and the EU are caught between upholding the deal and pressure from the US.
The European signatories believe the deal is the best way to limit Tehran's nuclear ambitions, while the US also wants Iran to stop meddling in the region and cease its missile programme.
The US has rushed an aircraft carrier, B-52 bombers and F-22 fighters to the region and Iran recently shot down a US military surveillance drone.
On Wednesday, Iran marked the day 31 years ago when the US Navy shot down an Iranian passenger jet in a mistake that killed 290 people and showed the danger of miscalculation in the current crisis.
The country ranks the tragedy alongside the 1953 CIA-backed coup that toppled Iran’s elected prime minister and secured Shah Mohammad Pahlavi’s absolute power until he abdicated the throne before the 1979 revolution.
Just after dawn on July 3, 1988, the USS Vincennes sent a helicopter to hover over Iranian speedboats that the navy said were harassing commercial ships.
It said the Iranians fired on the helicopter and the Vincennes gave chase, the US navy said.
But unacknowledged for years afterwards by the navy was the fact that the US warship had crossed into Iranian territorial waters in pursuit. It began firing at the Iranian ships there.
The Vincennes then mistook Iran Air flight 655, which had taken off from Bandar Abbas in Iran, for an fighter jet. It fired missiles, killing all on board.
The US later gave USS Vincennes' Capt William Rogers its Legion of Merit award, further angering Iran.
Iranian state television broadcast footage on Wednesday of mourners throwing flowers into the Strait of Hormuz as armed Iranian Revolutionary Guard boats patrolled around them.