Iran is set to detail its latest cut to commitments under a 2015 nuclear deal on Saturday, in response to US sanctions and perceived inaction by other parties to save the accord.
Iran's atomic energy organisation spokesman Behrouz Kamalvandi will hold a news conference on Tehran's third round of cuts in its nuclear commitments since May, the semi-official ISNA news agency reported on Thursday.
Iran and three European countries -- Britain, France and Germany -- have been engaged in talks to reduce tensions and rescue the multi-party deal, which has been unravelling since the US withdrew in May last year.
But with no apparent agreement in sight, Iran's President Hassan Rouhani on Wednesday made good on a promise to take another step away from the deal between Iran and the five permanent members of the United Nations Security Council powers, plus Germany (P5+1).
"The atomic energy organisation (of Iran) is ordered to immediately start whatever is needed in the field of research and development, and abandon all the commitments that were in place regarding research and development," said Rouhani, without elaborating.
Iran's arch-enemy Israel responded by calling for more international pressure on the Islamic republic.
"This is not the time to hold talks with Iran; this is the time to increase the pressure on Iran," said Israeli Prime Minister Benjamin Netanyahu.
The EU on Thursday urged Iran to backtrack on moves to drop its commitments under the deal, known as the JCPOA.
"These activities we consider are inconsistent with the JCPOA," said European Commission spokesman Carlos Martin Ruiz de Gordejuela.
"We urge Iran to reverse these steps and refrain from further measures that undermine the nuclear deal."
French foreign ministry spokeswoman Agnes von der Muehll echoed this saying: "Iran must abstain from any concrete action that does not conform with its commitments (and which) could impede de-escalation moves."
A senior US official on Wednesday ruled out any sanctions exemptions that would permit a French-proposed credit line, which Tehran says could bring it back to full compliance with the deal.
"We can't make it any more clear that we are committed to this campaign of maximum pressure and we are not looking to grant any exceptions or waivers," Brian Hook, the State Department coordinator on Iran, told reporters.
Iran's Foreign Minister Mohammad Javad Zarif responded by tweeting that the US Treasury was "nothing more than a JAIL WARDEN."
"Ask for reprieve (waiver), get thrown in solitary for the audacity. Ask again and you might end up in the gallows," he tweeted.
Iran has expressed mounting frustration at Europe's failure to offset the effects of renewed US sanctions in return for its continued compliance with the agreement.
But Britain said Tehran's moves to suspend limits on research and development were "deeply concerning".
"This third step away from its commitments under the nuclear deal is particularly disappointing at a time when we and our European and international partners are working hard to de-escalate tensions with Iran," a Foreign Office spokesperson said.
Tehran had already hit back twice with countermeasures in response to the US withdrawal from the deal.
On July 1, Iran said it had increased its stockpile of enriched uranium to beyond the 300-kilogramme limit set by the agreement.
A week later, it announced it had exceeded the deal's uranium enrichment limit of 3.67 percent.
The UN's nuclear watchdog, the International Atomic Energy Agency, said on August 30 that Iran's uranium stockpile stood at about 360 kilogrammes, of which just over 10 percent was enriched to 4.5 percent.
Rouhani has stressed that the countermeasures Iran has adopted are all readily reversible if the remaining parties to the deal honour their undertakings to provide sanctions relief.
The Iranian president on Wednesday gave Europe a 60-day ultimatum before Iran drops another commitment.
Francois Nicoullaud, a French former ambassador to Iran, said the moves to be detailed Saturday would likely focus on bringing on line new centrifuges for enriching uranium -- and would be "only partially reversible".
"Even if research is stopped, the intellectual gains are forever," he said.
But analyst Henry Rome argued that the moves appeared to be "provocative but reversible".
"Tehran is building leverage, not a bomb," said Rome, a specialist on Iran for the Washington-based Eurasia Group consultancy.
He added that the French initiative, meant to provide Iran with a multi-billion-dollar line of credit in exchange for returning to deal compliance, is "likely to wither away" because it requires Washington's approval.