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.

But Russia’s delegate to the Iran talks, Sergei A. Ryabkov, the deputy foreign minister, hinted in comments reported by the Interfax news agency Wednesday night that Russia might link the Ukraine and Iran issues as part of its own diplomatic leverage with the United States and European Union.