Foreign Minister Sergei Lavrov said world powers had questions "about what may be -- has been or is -- a military component to the nuclear programme.
"Iran has underscored its desire to fully agree this document (on clearing up the suspicions)," Lavrov told reporters.
"We think that our Iranian colleagues could be doing this a little faster."
His comments came as Tehran proposed Cairo as the venue for the next meeting with the so-called "P5+1" -- the five permanent UN Security Council members and Germany.
Those talks run in parallel with the ones Iran is holding with the UN's International Atomic Energy Agency (IAEA) and focus on slightly different issues.
A top Russian official had earlier said that Moscow expected the fourth round of top-level talks Iran has held with the "P5+1" in the past 10 months to happen in Istanbul by the end of February.
Russia has voiced repeated concerns over a lack of dialogue over a contested Iranian programme that most powers believe is focused on developing a nuclear bomb.
The Kremlin has also urged Western powers led by EU foreign policy chief Catherine Ashton to offer meaningful concessions in return for Iran's formal renouncement of deeper enrichment.
Lavrov on Wednesday once again warned against Western attempts to isolate Iran and expressed dismay that the two sides were still arguing about the proper venue for negotiations.
Iranian media earlier quoted Foreign Minister Ali Akbar Salehi as saying that Tehran had proposed that the next meeting be held in Cairo.