This article originally appeared in Foreign Policy's Middle East Channel on April 9, 2012

BERLIN - If at one time European governments believed the threat of a nuclear-armed Iran was far more frightening for the United States than for those across the Atlantic, those days are in the past. As talks near on Iran's nuclear program, Tehran should know that European officials' views are somewhere in the middle between America's caution and Israel's alarm.

This major shift among European states was on display during a recent closed-door meeting in Berlin, organized by the Heinrich Boell Stiftung, the political foundation affiliated with Germany's Green Party. Not only did officials and experts agree with many in the Obama administration that the policy of containment has failed, all backed the demand that Iran must agree in upcoming talks scheduled for April 13 with the 5+1 permanent members of the United Nations Security Council to stop enriching uranium for a certain period.

European Union officials cited Iran's lack of transparency with the International Atomic Energy Agency as the reason enrichment should stop immediately and be allowed to resume only when Iran is in full compliance with the Nuclear Non-Proliferation Treaty. They also expressed intolerance for Iran's negotiating strategies -- which often involve presenting the same proposals, which have previously been rejected, as if they are something new.

If Iran does not agree to this concession and others, one European policy expert suggested, the renewed diplomatic process must stop immediately.

All of these demands on Iran -- including tough EU sanctions -- reflect a fundamental shift in the positions of EU member states. Therefore, it would be wise for the Iranian government to realize before attending the upcoming talks in Istanbul, that this time things will be different. The Europeans, like the Americans, will not be content with promises for more talks or the usual conflicting statements coming from Iranian nuclear negotiators or Iranian intransigence. As Catherine Ashton, Europe's top diplomat, said in a recent interview with Der Spiegel: "We don't want talks for the sake of talks. We need tangible progress."

Although the Europeans attending the meeting said they categorically reject a military attack on Iran just as they are not seeking regime change, they also stated that Iran's political elites, centered around Supreme Leader Ali Khamenei, are too unpredictable to be in possession of a nuclear weapon.

So how far is Europe willing to go to prevent a nuclear-armed Iran? Much like the Obama administration, the hope of some states is that tough sanctions and an oil embargo will be enough to persuade Iran to reach a negotiated settlement. The EU estimates the embargo will cost Iran to lose one-quarter of its income.

Public opinion in Europe and the United States also seems to be in sync. The Transatlantic Trends by the German Marshall Fund (GMF) have been showing in the past few years that European and American publics are similarly concerned about Iran acquiring nuclear weapons. In 2011, 76 percent of Americans and 75 percent of Europeans said they were concerned about Iran acquiring nuclear weapons.

European governments in the past were perceived to be soft on Iran, even though some EU member states' positions were complex. First, a few years ago, it took heavy lobbying by the Bush administration to get the Europeans on the same page regarding economic sanctions. But at the same time, Chancellor Angela Merkel of Germany made clear in her speech to the Knesset in 2008 that for her "Israel's security will never be open to negotiation." In 2009, European diplomats welcomed the efforts for more diplomacy by the newly elected President Barack Obama. To Europeans, it looked like the U.S. administration was moving closer to their views.

But now, it appears some states have come full circle. The European Union was just as eager to sanction Iran as the Americans. For the Europeans, tightening sanctions is the only option left to avoid an Iranian nuclear bomb and a military escalation.

As all parties approach the nuclear talks in Istanbul, Iran should know that the West stands united and if no resolution is reached, the United States and European states will have two calculations in which to make a decision about a military attack: Is the nuclear clock ticking faster than the effect of sanctions on the Iranian regime? And if so, would the potential damage from a nuclear attack on Iran and the region be less or greater than a nuclear-armed Iran?