When Russia and Iran last month announced that they had signed a contract for the Russian nuclear energy firm Rosatom to build more nuclear power reactors in Iran, some observers saw it as a bad sign for the nuclear negotiations underway in Vienna. After all, if Iran was preparing to sign a nuclear deal with six world powers, why was it enlisting Russia to build more nuclear power stations before the terms of the deal were even agreed?

But US and Western officials and experts say the prospective Russia-Iran energy deal may help resolve one of the toughest issues in the nuclear talks — the size of Iran’s enrichment capacity in a final deal — and they have recently gone out of their way to praise the Russian role in the sensitive nuclear negotiations as being highly constructive, professional and creative.

Much of that rare U.S. praise for Russia extends to Moscow’s lead Iran nuclear negotiator, Deputy Foreign Minister Sergey Ryabkov. The 54-year-old career diplomat has managed to maintain a constructive working rapport with US and European counterparts at the Iran negotiating table, despite the deep strains plaguing Moscow-West relations over Ukraine.

Ryabkov is “a very skillful, professional diplomat who represents Russian interests very well,” Robert Einhorn, a former top member of the US-Iran nuclear negotiating team, told Al-Monitor. “And he has played a very constructive role in these negotiations including in the recent period.