Under the current conditions achieving an agreement will be very tough, unless a new move is made, Russian Deputy Foreign Minister Sergei Ryabkov said here Thursday.
"The negotiations are pursued amid a very serious atmosphere, full of tension," said Ryabkov according to the IRNA reporter here, in an interview with his country's news agency.
He added that the time is flying and multilateral meetings are being held in Vienna.
Iran Foreign Minister's Deputies Majid Takht-e-Ravanchi and Seyed Abbas Araqchi held quadrilateral meeting with representatives of Germany, UK and France on Thursday.
The quadrilateral meeting was held prior to the arrival of US Secretary of State John Kerry to Vienna aimed at joining the talks.
Iranian Foreign Minister Mohammad Javad Zarif, the EU nuclear coordinator Catherine Ashton and US senior diplomat William Burns also held trilateral talks in Vienna on Thursday.
The nuclear talks between Iran and members of the G5+1 (US, Britain, Russia, France and China plus Germany) will end on November 24, the deadline to reach a comprehensive settlement.