Iran has been accused of making “maximalist demands” in the latest unsuccessful round of talks on reviving the nuclear non-proliferation deal at a grave session of the UN security council in which it was widely acknowledged that the talks – and the whole 2015 deal – were on the brink of collapse.

Iranian and US officials, with the EU acting as mediators, held two days of talks in Doha in a bid to break a months-long impasse, but no progress was made on Iran’s central demand that the Islamic Revolutionary Guard Corps be removed from US sanctions and its list of foreign terrorist organisations.

“Not only has Iran not taken up the offer on the table, but it also added yet more issues which fall outside the JCPOA [Joint Comprehensive Plan of Action] with maximalist and unrealistic demands,” the French ambassador to the UN, Nicolas de Rivière, said on Thursday.

The broader talks have been stalled since March, but the recent fresh restrictions placed on UN weapons inspectors – as well as Iran’s speeding up of uranium enrichment – has injected a sudden urgency into the crisis. Western leaders will have to take decisive steps including reimposing UN sanctions in weeks if the nuclear inspectorate continues to be unable to carry out its monitoring duties.

During the special session of the UN security council, Barbara Woodward, the UK envoy, warned Iran that no better deal was going to be offered.

Olof Skoog, the EU’s ambassador to the UN, said: “I am concerned that we might not make it over the finishing line. My message is: seize this opportunity to conclude the deal, based on the text that is on the table. The time to overcome the last outstanding issues, conclude the deal and fully restore the [agreement] is now.”

The context of the impasse – growing Iranian enrichment and ballistic missile activity – is also concerning European leaders.

Woodward warned: “Iran’s nuclear programme has never been more advanced than it is today and Iran’s nuclear escalation is a threat to international peace and security.”

“At the current enrichment rate, by the end of this year, Iran is likely to have enough enriched material to rapidly produce highly enriched uranium at 90% enrichment for several nuclear devices,” she said. “Iran also continues to develop ballistic missiles in a way that is inconsistent with UN resolutions.”

In a joint statement, Germany, France and the UK claimed that Iran was testing ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic missile technology. The statement said: “Only a few days ago, Iran conducted another test of a space launch vehicle, which contains dual-use technology that can be used to construct long-range and intercontinental ballistic missiles.”

The Iranian ambassador, Majid Takht-Ravanchi, said an agreement was “not out of reach” but that success required significant changes in US policy, specifically regarding the imposition of sanctions. He also said guarantees were needed that the US would not leave the deal again as they had under Donald Trump in 2018.