US Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif have met for two hours in Geneva in another round of nuclear talks to try to narrow gaps as they pressed against a March 31 deadline to reach a political agreement.
Sunday's meeting included for the first time US Secretary of Energy Ernest Moniz and Iran's nuclear chief Ali Akbar Salehi, who spent most of the day separately negotiating technical details of curbing Iran's nuclear programme.
The talks are set to resume on Monday before Kerry returns to Washington in time to testify before the Senate foreign relations committee on Tuesday on the State Department's 2016 budget request.
Zarif told Iranian state media that mid-level bilateral talks had produced "good discussions but no agreements", and some differences remained.
"The fundamental gap, in my view, is psychological. Some Western countries, the United States in particular, see sanctions as an asset, a lever to exert pressure on Iran. As long as this thinking persists it will be very hard, difficult to reach a settlement."
Zarif said the inclusion of Moniz and Salehi reflected a need "for higher level people with all-embracing command over all issues". The presence of a close aide and the brother of Iranian President Hassan Rouhani, Hossein Fereydoon, meant better "coordination with the president", he added.
The talks took place behind closed doors with no customary photo opportunity for journalists covering the meetings.
'Distance to travel'
Kerry on Saturday cautioned against reading too much into the presence of Moniz in Geneva, which US officials said was decided after Iran announced Salahi would attend. "There is still a distance to travel," he told a news conference in London.
The negotiations between Iran and P5+1 powers - including the United States, Britain, Germany, Russia and China - have reached a sensitive stage with divisions remaining, mainly over Iranian uranium enrichment and the pace of removing sanctions.
A recent UN report said Iran had refrained from expanding tests of more efficient models of a machine used to refine uranium under a nuclear agreement with the six world powers. Development of advanced centrifuges is feared to lead to material potentially suitable for manufacture of nuclear bombs, which Iran says it does not intend to develop.
Kerry said US President Barack Obama was not inclined to extend the talks again after the parties already missed a November 2014 target date.
Obama believed it was "imperative to be able to come to a fundamental political outline and agreement within the time space that we have left", the secretary of state said.
Zarif said Rouhani would not accept a small, short-term agreement, nor a broad accord that left room for interpretation.