Russia's largest banks seek to reassure investors over E.U. moves that cut off access to capital markets, while Moscow announces bans on certain E.U. food imports. (Reuters)

When the United States first threatened Russia with sanctions in April, Iranian officials reportedly cautioned the Kremlin against ignoring the American warnings. Having experienced the effect of such restrictions on their own country, the Iranians apparently advised Russia not to underestimate the possible impact.

This week, the United States and the European Union imposed their strictest sanctions yet on Russia. Nevertheless, Russian officials seem confident that their nation would weather the storm. The most important questions now are: How long and how many measures will it take for Russia to feel the pressure? And even if the effects become visible — how much pressure will it take for Russia to change its policy on Ukraine? The Iranian example could be illuminating.

There are some obvious similarities between Iran and Russia: Oil is an important source of revenue for both countries, and they behaved similarly confident when the danger of tougher sanctions loomed. In 2009, Iranian President Mahmoud Ahmadinejad called U.S. sanctions "childish"; Russian President Vladimir Putin criticized the United States earlier this year, saying that sanctions would be "harmful to the national long-term strategic interests of the American state, the American people."

When international pressure on Iran increased in 2009, the country could already look back at decades of experience with U.S. sanctions that had been imposed after the seizure of the American Embassy in Tehran in 1979. “There was a sense of overconfidence. The Iranians did not expect that major international sanctions could be imposed without a serious backlash on the West,” says Suzanne Maloney, a senior fellow on Iran at the Brookings Institution. But the Iranians had underestimated the power of concerted international sanctions. While OPEC’s oil production got back on track after the 2008 crisis, Iran’s exports and revenue declined. Sanctions took about half of Iran’s oil exports offline and cut off Iranian banks from the rest of the world.

(Sources: U.S. Energy Information Administration, International Energy Statistics Database and Iran Country Analysis Brief)

The shock waves were massive: Iran’s economy contracted in 2012 and 2013, with the inflation rate topping 40 percent. Consequently, political debates began to emerge that led to the current negotiations on Iran’s disputed nuclear program, though their outcome is still uncertain. Could the same strategy work on Russia?

Although numerous sanctions against Russia had already been announced, this week’s measures appeared to show a clear upgrade in targets. The largest state banks and Rosneft, the state oil company, are on the sanctions list. Apart from that, the E.U.’s measures are now at a level similar to those of the United States, which means that Russian companies and banks will have to look eastward for funding. Is that enough to force Putin to back away from Ukraine? Sergei Guriev from Sciences Po in Paris claims that the only substantial sanctions so far are not the most recent ones but those implemented in March — “simply because they created a precedent."

"Today's sanctions will not be catastrophic for the Russian economy and Russian citizens in the immediate future,” he says.

Furthermore, Russia’s economy is much more integrated into the global economy than Iran’s. Confronted with new sanctions, Russia could decide to retaliate and confiscate companies’ foreign direct investments in the country. And we shouldn’t forget that the country produces about three times as much oil as Iran and supplies 30 percent of the gas consumed by the E.U.

Cliff Kupchan — who has studied both Russia and Iran — thinks that sanctions could nevertheless have a certain impact. "Putin and Russia are vulnerable because the economy was floundering even before the Ukraine episode," he said. Growth predictions for Russia have indeed worsened over the past months:

Growth predictions for Russia have constantly fallen. (Source: DIW Berlin).

Are Europe and the United States willing to risk the backlash from their sanctions? Even if they are, they may have to put up with that risk for quite some time — Russia’s Reserve Fund and its National Wealth Fund would be equipped to help the country out in the short run, and its economy will prove to be more resilient than Iran’s.

Barry W. Ickes, a professor at Pennsylvania State University, predicts that ultimately it will come down to a test of wills: “For whom is Ukraine more important? And who is willing to suffer the most for it?”