European and American officials have voiced doubt about restoring the 2015 Iran nuclear deal after indirect talks between Washington and Tehran failed this week.

A European Union official said the negotiations with Iran "might not make it over the finishing line" and a US official expressed the view that the odds had lengthened after two days of talks in Qatar.

The UN Security Council met to discuss Iran one day after the talks ended in Doha with no sign of progress on resurrecting the pact.

"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," European Union Ambassador to the United Nations Olof Skoog said.

The EU coordinates the talks on resurrecting the agreement, which then US President Donald Trump reneged on in 2018 and restored crippling US sanctions on Iran, prompting Tehran to start violating its nuclear restrictions about a year later.

"The prospects for a deal after Doha are worse than they were before Doha and they will be getting worse by the day," the senior US official told Reuters on condition of anonymity.

"You could describe Doha at best as treading water, at worst as moving backwards. But at this point treading water is for all practical purposes moving backwards," he added.

The Security Council met to discuss the latest report by UN Secretary-General Antonio Guterres on the implementation of a 2015 council resolution that enshrines the nuclear deal, formally called the Joint Comprehensive Plan of Action (JCPOA).

US, British and French diplomats all placed the onus on Iran for the failure to revive the agreement after more than a year of negotiations.

Iran "should urgently take this deal - there will not be a better one," Britain's U.N. Ambassador Barbara Woodward said.

Iranian government media on Friday carried headlines saying the exact opposite, that the onus is on the US to provide more guarantees over the longevity of the deal and more economic benefits.

The US says that in December a final offer was made to Iran, and it will not accept Tehran’s attempts to introduce new elements into the negotiations and make demands “extraneous” to the nuclear issue.

When after 11 months of talks in Vienna the process came to a halt, it became apparent that Iran was demanding the removal of its Revolutionary Guard from the US Foreign Terrorist Organization list. Washington says that is not one of the sanctions related to the nuclear issue.

"Iran has yet to demonstrate any real urgency to conclude a deal, end the current nuclear crisis and achieve important sanctions lifting," Richard Mills, Deputy US Ambassador to the United Nations, told the meeting.

"Not only has Iran not taken up the offer on the table, but it also added yet more issues which fall outside the JCPOA with maximalist and unrealistic demands," French U.N. Ambassador Nicolas de Riviere said.

Iran, however, described the latest talks as "serious and positive" and said it was ready to strike an agreement.

"Iran has demanded verifiable and objective guarantees from the US that JCPOA will not be torpedoed again, that the US will not violate its obligations again, and that sanctions will not be re-imposed under other pretexts or designations," Iran's UN Ambassador Majid Takht Ravanchi told the council.

The senior US official disputed Tehran's argument that Washington was to blame for the lack of progress, saying the United States had responded positively to proposed EU changes to the draft text of an agreement reached in wider talks in March while Iran had failed to respond to those proposals.

"Their vague demands, reopening of settled issues, and requests clearly unrelated to the JCPOA all suggests to us ... that the real discussion that has to take place is (not) between Iran and the US to resolve remaining differences. It is between Iran and Iran ," the senior US official said.

"At this point, we are not sure if they (the Iranians) know what more they want. They didn’t come to Doha with many specifics," he added.

However, Chinese and Russian diplomats faulted the United States, with Beijing's representative urging Washington to ease unilateral US sanctions on Iran and Russia's calling for all sides to show flexibility.

Reporting by Reuters