Russia signed a deal Tuesday to build new nuclear reactors in Iran as another round of talks that aim to prevent the Islamic Republic from obtaining atomic weapons ended without a breakthrough.

The deal foresees the expansion of the existing Bushehr plant with two reactors and an option for two more, as well as four units elsewhere, according to an emailed statement by Moscow-based Rosatom Corp. U.S. Secretary of State John Kerry, former European Union foreign policy chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif ended two days of talks in Oman Monday without reporting progress.

"There wasn't any discussion on uranium enrichment in Iran, either in the negotiations or the documents" signed, Sergei Novikov, a spokesman for state-owned Rosatom, said by phone. "All we are offering is the localization of some equipment needed for construction."