“It is too early to say whether Iran has returned to this round with a constructive approach,” RIA Novosti Price quoted as saying.
He called the progress in the negotiations "modest", noting that "it is too early to say how substantive it is."
The State Department also added that Iran is moving too slowly to return to the JCPOA.
Earlier, Russia's Permanent Representative to international organizations in Vienna, Mikhail Ulyanov, announced "undeniable progress" in the negotiations on the JCPOA.
On December 27, the heads of the Russian and US delegations met before the start of the eighth round of consultations on the restoration of the Iranian nuclear deal.