European powers Thursday denounced Tehran’s threat to resume nuclear work, provoking a swift rebuke from the Iranian foreign minister, who accused them of being weak in the face of US bullying.

The three European signatories to the 2015 Iran nuclear deal urged the Islamic republic to honor its commitments after it said it would cease to respect some of the limits imposed by the agreement.

They also rejected an ultimatum from President Hassan Rouhani, who threatened to go further if they fail to deliver sanctions relief to counterbalance US President Donald Trump’s renewed attack on the Iranian economy within 60 days.

EU diplomatic chief Federica Mogherini and France, Germany and Britain – the three European signatories to the agreement – expressed “great concern” at Rouhani’s dramatic intervention.

“We strongly urge Iran to continue to implement its commitments under the JCPOA in full as it has done until now and to refrain from any escalatory steps,” they said in a joint statement, referring to the Joint Comprehensive Plan of Action as the agreement is known.

“We reject any ultimatums and we will assess Iran’s compliance on the basis of Iran’s performance regarding its nuclear-related commitments under the JCPOA.”

Iranian Foreign Minister Mohammad Javad Zarif hit back on Twitter, scornfully dismissing the European communique.

“EU statement today is why JCPOA is where it is: the US has bullied Europe – and rest of world – for a year and EU can only express ‘regret’,” Zarif tweeted.

“Instead of demanding that Iran unilaterally abide by a multilateral accord, EU should uphold obligations,” he said, calling for the “normalization of economic ties.”

Tehran says its announcement on Wednesday was a response to unilateral American sanctions – imposed since Trump ripped up what he called a “horrible” deal – which have dealt a severe blow to the Iranian economy.

Europe has stressed the importance of the deal – in which Iran agreed to curb its nuclear ambitions in return for sanctions relief – for its own security, and EU leaders discussed the crisis at their summit in the Romanian town of Sibiu.

Russia, another signatory to the deal along with China, on Thursday denounced new US sanctions on Iran’s mining industry and called for talks to preserve the deal.

Moscow said it understood why Iran had decided to suspend some of its commitments under the deal in the face of US sanctions but urged Tehran not to go further.

French President Emmanuel Macron appealed for calm, saying Europe must work to convince Iran to adhere to the agreement.

“We must not get jumpy or fall into escalation,” Macron said, warning that leaving the deal would “unstitch what we have achieved.”

He added, “That’s why France is staying in and will stay in, and I profoundly hope Iran will stay in.”

The EU statement stressed the International Atomic Energy Agency’s (IAEA) role in monitoring Iran’s compliance with the deal – suggesting no concrete action is likely until the inspectors’ next report at the end of May.

– with reporting by AFP