The problem of Iran's nuclear centrifuges also remains an issue of concern, according to Ryabkov. The diplomat noted that during the previous rounds of Iranian nuclear talks the negotiators agreed that Iran has to limit its uranium enrichment to five percent.

The Russian deputy foreign minister said that he had a number of bilateral meetings with members of the sextet and the Iranian side. A coordinating meeting among the nations of the P5+1 group - China, France, Germany, Russia, the United Kingdom and the United States - is due to take place later on Thursday, on the eve of the next round of nuclear talks, according to Ryabkov.

“It feels like there is a common understanding that every effort has to be made to reach an agreement,” the diplomat said.

“Flexibility is needed to form a framework, a carcass of agreement. As of the Russian delegation, we have this flexibility, but also our ‘red lines’, which is normal,” Ryabkov added.

The new round of nuclear negotiations between Iran's political leadership and the 5+1 group is due to take place in New York on September 18-22.

On November 24, 2013, an action plan was adopted in Geneva, according to which Iran and the so-called P5+1 international mediation group had to reach an agreement that would guarantee the peaceful nature of Tehran’s nuclear program in exchange for lifting international sanctions previously imposed on Iran.