A top Russian diplomat says the Vienna talks have "picked up speed" and chances for reviving Iran’s nuclear deal, the JCPOA have increased, but problems remain.

Deputy Foreign Minister Sergei Ryabkov said that the talks have gained momentum as all the participants are showing readiness to find solutions for the remaining problems. Expansion of Tehran’s nuclear program and issues related to US sanctions are still hindering the process, he added.

Ryabkov maintained that the ultimate goal is a return to the implementation of the JCPOA in its original parameters and various schemes are possible for that, including a step-by-step approach based on reciprocity.

“I emphasize that hypothetical intermediate steps are not a replacement, not a substitution, not an alternative to the basic agreement, which must be restored in full”, Ryabkov said without elaborating.

Russia’s top negotiator Mikhail Ulyanov tweeted on Tuesday that the talks are being held in “varying geometry” as the need arises, but nobody is left behind.

On Monday, Iran’s foreign ministry spokesman said Tehran is not satisfied with the pace of nuclear talks in Vienna but would not accept deadlines.

"Time is important to us, but it is not possible that the other side moves like a turtle and we move at the speed of light," Saeed Khatibzadeh said, adding that Tehran wants a “sustainable and reliable” agreement.