The three European parties negotiating revival of the 2015 Iran nuclear deal warned Russia on Tuesday not to complicate efforts to reach an accord.

In joint statement to the International Atomic Energy Agency’s Board of Governors, France, Germany and the United Kingdom called on Moscow not to “add extraneous conditions.”

Russian foreign minister Sergei Lavrov said Saturday Moscow was looking for guarantees that any sanctions against Russia over Ukraine would not affect “the regime of trade-economic and investment ties embedded in the Joint Comprehensive Plan of Action [the 2015 deal] on the Iranian nuclear program.”

With talks in Vienna over JCPOA revival between Iran and six world powers – the western European trio (E3), China, Russia and the United States – reportedly nearing their end, the Ukraine crisis has cast a shadow.

The E3 said the Vienna talks were “very close to finalizing a deal that would address our most pressing and immediate non-proliferation concerns, returning Iran’s nuclear programme [sic] to JCPOA limits as well as restoring…transparency measures…The window of opportunity is closing.”

The statement called on Iran to return to limits over uranium enrichment prescribed by the 2015 deal and to prepare “to dispose of its stockpile of enriched uranium in excess of JCPOA limits.” It has been widely assumed Russia would ship out the latter.