"All the parties need to build bridges over still deep gaps on issues like enrichment, like sanctions," Russia's Deputy Foreign Minister and chief nuclear negotiator Sergey Ryabkov told journalists in Muscat.
While the Iranian officials were engaged in talks with members of the P5+1 - US, UK, France, Russia, China and Germany - on Tuesday, a 'reasonably optimistic' Ryabkov made an unscheduled appearance at the media centre and spoke candidly about the talks.
"The glass is not half empty. We are reasonably optimistic but not to an extent that we are sure that this agreement can be achieved. It is really a unique and never tried before effort," he said.
"There is a chance, there is no reason to be negative or pessimistic. We are confident we will be able to achieve this goal," Ryabkov, who participated in the last leg of talks in Muscat on Tuesday, said.
The Russian negotiator urged Iran and the participants in the talks 'not to kill the chances' of a comprehensive deal by the November 24 deadline. "If by whatever reason, by whatever development, we are not there, I think we will have time on the evening of the 23rd (a day before the deadline to achieve a final deal expires) to develop an alternative," said Ryabkov.
"We are not working on Plan B," he added.
Lavrov calls Kerry
On Wednesday, Russia's Foreign Minister Sergey Lavrov called his US counterpart John Kerry - who had participated in the two-day intense dialogue with Iran's Foreign Minister Mohammad Javad Zarif and EU negotiator Catherine Ashton in Muscat on Sunday and Monday. Both Lavrov and Kerry called for a final agreement to be reached 'as soon as possible'
"The need to reach as soon as possible a comprehensive agreement which would allow to fully normalise the situation around the Iranian nuclear programme has been acknowledged," the Russian foreign ministry said.
In a related development, Russia signed a contract on Tuesday for building two reactors at Iran's first Moscow-built nuclear plant in Bushehr.
Sergey Kiriyenko, the head of Russia's Rosatom state corporation, and Iran's nuclear chief Ali Akbar Salehi also signed a protocol envisaging possible construction of two more reactors in Bushehr and another four in an undetermined location.
"It's a turning point in the development of relations between our countries," Salehi said after the signing, according to Russian news reports.
Rosatom said in a statement that the construction of the new reactors will be monitored by the International Atomic Energy Agency.