The chances of reviving the 2015 Iran nuclear deal are worse after indirect US-Iranian talks in Doha that ended without progress, a senior US official told Reuters on Thursday.

"The prospects for a deal after Doha are worse than they were before Doha and they will be getting worse by the day," said the official 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."

After a pause in the 11-month-long Vienna round of nuclear talks in March, the European Union foreign policy chief Josep Borrell visited Tehran on June 25 and arranged the talks in Qatar.

The official would not go into the details of the Doha talks, in which European Union officials shuttled between the two sides trying to revive the 2015 Joint Comprehensive Plan of Action (JCPOA) agreement under which Iran had limited its nuclear program in return for relief from economic sanctions.

"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," he said. "It is between Iran and Iran to resolve the fundamental question about whether they are interested in a mutual return to the JCPOA."

Report by Reuters