Iran and Russia are in negotiations over the construction of a second nuclear power plant in Bushehr province, according to a senior Russian official.

The deputy head of the Russian State Atomic Energy Corporation (Rosatom) Nikolai Spassky said the talks were at a “working stage.”

“We are discussing the possibility of continuing our cooperation with Iran,” he added in comments quoted by RIA Novosti. “Any partnership if we agree, must and will comply with Russia’s international obligations and should be cost-effective.”

Iran’s semi-official Fars News Agency carried Spassky’s comments with the headline: “Official: Russia to Help Iran Build 2nd N. Power Plant in Bushehr,” implying that negotiations were further along than the Russian official indicated. Iranian President Hassan Rouhani had announced plans to build a second reactor in Bushehr in December.

In related news, Moscow panned on Friday Washington’s expansion of existing Iran sanctions lists.

On Thursday, the US Treasury and State Departments announced the addition of several individuals and firms to those lists, a move which the Russian Foreign Ministry called “unacceptable.”

In a statement, the ministry said the expansion of sanctions went against the progress of ongoing negotiations over the Islamic Republic’s nuclear program.

“We have said repeatedly that such decisions contradict the spirit of the Geneva agreements, where it is stipulated in particular that Washington refrains from introducing new sanctions related to the nuclear activities of Tehran,” the statement read.

“We consider the step made to be unacceptable and that it contradicts international law.”

As part of an interim deal reached in November, Iran must largely suspend progress on its nuclear program in exchange for limited sanctions relief. The US Congress has been mulling additional sanctions legislation that would go into effect should Tehran fail to comply with the terms reached in Geneva, a measure which the Obama administration strongly opposes.