Moscow: Talks on Iran's nuclear programme are being held in a tense atmosphere and getting a deal will be very difficult, Russia's chief negotiator told Russian agency RIA Novosti as a deadline loomed.
"In the current situation it will be very difficult to get a deal unless there is a new spirit," Sergei Ryabkov was quoted as saying. "The talks are being held in a tense atmosphere".
"Time is passing and there are constant meetings in all formats. Perhaps to resolve the problems as they crop up in the talks the delegations need to receive additional instructions" from capitals, he said.
He warned: "A possibility like we have at the moment (to get a deal) is very rare. This is a crucial moment and to let it pass would be a serious mistake with grave consequences."
Iran and six world powers have until Monday to agree a mammoth deal that eases fears once and for all that Iran might develop nuclear weapons under the guise of its civilian programme -- an ambition it hotly denies having.
The comments came as US Secretary of State John Kerry arrived in Vienna to join the talks.