Despite public assurances by Western officials, concern is growing that the escalating animosity between the United States and Russia over the Ukraine crisis could have a corrosive effect on the nuclear talks with Iran.
Even before the Obama administration expanded the scope of sanctions on Thursday over Russia's annexation of Ukraine's Crimean Peninsula, the Russians had sent signals that their retaliatory tools might include an altered position regarding the Iran talks, in which Russia and the United States are colleagues in the six-nation group negotiating with the Iranians.
Two days of talks in Vienna concluded on Wednesday, with another round scheduled to begin April 7. Both sides said the talks had been constructive.
"I'm personally deeply concerned that the Russians are going to move ahead, if not with this deal, then some other sanction-busting scheme," said Mark Dubowitz, the executive director of the Foundation for Defense of Democracies, a Washington-based group that has advocated tough sanctions on Iran.
"If you're Putin and you think you're going to be a target of sanctions, the most obvious leverage is in the Iranian file, where Russian cooperation is so important," Mr. Dubowitz said.