Earlier this week, officials and diplomats apparently emerged from the latest round of nuclear-drawdown talks between Iran and six world powers — the United States, Germany, China, France, Britain, and Russia — without having made much progress beyond agreeing to meet again in April, but cautiously optimistic that Russia’s aggression with Ukraine wasn’t doing anything to undermine the discussions.

That was yesterday. Then this happened.

Russia may revise its stance in the Iranian nuclear talks amid tensions with the West over Ukraine, a senior diplomat warned Wednesday. …

Russia has cooperated with the United States and other Western nations in the Iranian talks, but [Deputy Foreign Minister Sergei] Ryabkov warned that its attitude may now change.

“We wouldn’t like to use these talks as an element of the game of raising the stakes taking into account the sentiments in some European capitals, Brussels and Washington,” Ryabkov was quoted as saying by Interfax. “But if they force us into that, we will take retaliatory measures here as well. The historic importance of what happened in the last weeks and days regarding the restoration of historical justice and reunification of Crimea with Russia is incomparable to what we are dealing with in the Iranian issue.”

How nice. I don’t know who is honestly expecting much from these Iranian deal-making sessions (beyond giving Iran the opportunity to stall and bloviate while they receive their sought-after sanctions relief, of course), but one gets the feeling that Russia is ready to start being deliberately unhelpful, no?

“If President Putin goes ahead with his apparent intention to annex Crimea, we’re going to have to sanction Russia, and they are going to have to retaliate, and it’s really going to screw up the P5-plus-one negotiations with Iran,” said Gary Samore, a former senior aide on nonproliferation on the National Security Council in President Obama’s first term. He is now executive director for research at Harvard’s Belfer Center for Science and International Affairs, as well as the president of United Against Nuclear Iran, a group that advocates strong sanctions against Iran until the nuclear dispute is resolved.

“The problem will be that Iran will feel much less pressured to make any concessions if they think the P5-plus-one are squabbling,” Mr. Samore said. “The Iranians will be watching and waiting; they are not inclined to make any concessions anyway, but they are going to be less inclined until there is a resolution” of the situation in Ukraine.