Iran had "intense and tough" talks on Monday with the six world powers concerned about its nuclear programme, but there was no clear progress towards ending a decade-long dispute which risks sparking a new Middle East war.
A spokesman for the head of the delegation talking to Iran held out hope for a result on the second, final day of talks.
"We had an intense and tough exchange of views," said European Union foreign policy head Catherine Ashton's spokesman Michael Mann. "We agreed to reflect overnight on each others' positions."
Al Jazeera's Robert Forrestier-Walker reports from Moscow.
