France, Britain and Germany on Saturday said they had "serious doubts" about Iran's intentions to revive a nuclear deal, comments that were rejected by Tehran and called "very untimely" by Moscow.
Iran earlier this month sent its latest response to the European Union's proposed text to restore the 2015 agreement under which Tehran had restrained its nuclear programme in exchange for relief from US, EU and UN economic sanctions.
Diplomats have said Iran's response to the EU coordinator was a step backwards, with it seeking to link a revival of the deal with the closure of investigations by the International Atomic Energy Agency (IAEA) into uranium traces at three sites.
The IAEA's Board of Governors meet on Monday, three months after adopting a resolution urging Iran to give credible answers to the watchdog on the issue. Ahead of that meeting the European parties to the deal vented their frustration.
"This latest demand raises serious doubts as to Iran's intentions and commitment to a successful outcome on the JCPoA," the three countries, known as the E3, said in a statement, referring to the deal's full name, the Joint Comprehensive Plan of Action.
"Iran's position contradicts its legally binding obligations and jeopardises prospects of restoring the JCPoA."
Iran's Foreign Ministry spokesperson Nasser Kanaani said the statement was "unconstructive", adding "the three European countries are advised to play a more active role in providing solutions to end the few disagreements that remain", state media reported.
"If such an approach persists, they (E3) should also take responsibility for its consequences," Kanaani said without elaborating.
The European statement also prompted Russia's envoy to the talks to respond on Twitter calling it "very untimely indeed". He dismissed the perceived blockage as something that "was not a serious obstacle".
Highlighting how entrenched positions are before next week, France's negotiator, Philippe Errera, called out his Russian counterpart.
"There is no longer an active negotiation, since Iran's last response - which you, unlike almost all your followers, have had access to," he said on Twitter.
Ulyanov responded that at least they agreed that there was no active negotiation.
Then-US President Donald Trump abandoned the deal in 2018 and re-imposed US sanctions, prompting Iran to start breaching the deal's nuclear curbs and reviving US, Arab and Israeli fears it may be seeking an atomic bomb. Iran denies having nuclear ambitions.
The IAEA said on Wednesday Iran's stock of uranium enriched to up to 60%, close to weapons-grade, had grown to enough, if enriched further, for a nuclear bomb and that Tehran had still failed to explain the origin of the uranium particles.
"Given Iran’s failure to conclude the deal on the table, we will consult, alongside international partners, on how best to address Iran’s continued nuclear escalation and lack of cooperation with the IAEA regarding its NPT (non-proliferation treaty) safeguards agreement," the E3 said.
It is unclear at this stage how the Western powers will respond, although diplomats said a new resolution at the IAEA was unlikely.