Brussels - With a US decision looming whether to leave the Iran nuclear deal, the European Union has several options and scenarios to ponder, however, one thing is clear: the bloc will likely have to reckon with a break in EU-US relations. The EU has been trying to convince US President Donald Trump, a fierce critic of the 2015 deal with Iran, to stick with the agreement. Trump is due to announce Tuesday whether to reintroduce US sanctions on Iran - possibly spelling an end to the accord.

A "huge blow" to the EU

Seeing the US scrap the agreement would be a "huge blow" to the EU, said Ali Vaez, director of the Iran Project at the International Crisis Group, a non-governmental organization dedicated to preventing crises. "This is one of the rare concrete achievements of EU multilateral diplomacy in the past years," Vaez told dpa. "If the EU caves in facing US pressure, it not only demonstrates that it cannot defend any agreement that it has persistently assessed as critical to its own security, but it also demonstrates that the EU basically does not have an independent foreign policy."

EU-US relations in a breaking point?

Cornelius Adebahr, an expert with the think tank Carnegie Europe, said that the fate of the Iran deal might actually bring EU-US relations to a breaking point - after trust has already been weakened by Trump's other actions, including pulling out of the Paris climate deal and criticizing NATO. "I see this as a part of a broader realization of how much the Europeans and the Americans - actually, the American government, I should say - stand next to one another," Adebahr said. The US ripping up the deal would pose "some fundamental questions" about the EU-US relationship, he noted. "The question is whether the Iran file is indeed a moment for the Europeans to position themselves and say, 'No, this is our red line'," Adebahr said. It is, of course, far from certain what Trump will actually decide to do with the Iran deal: his options range from keeping the deal intact to weakening it or leaving it altogether. "I don't actually expect him to rip up the deal in the coming days," Adebahr said, noting that it wouldn't make sense for Trump to fully stick with the deal either. "By neither going all in or all out, but by letting the deal barely survive, he can keep up the pressure on Europeans."

Plan B

The EU is working on a Plan B to help businesses continue to operate in Iran if Washington reimposes sanctions, a senior EU official said. The aim is to make sure it remains in Tehran's interest to keep complying with the deal. Vaez of the International Crisis Group said the EU needs to protect European businesses from possible US sanctions and give Iran a financial incentive to stick with the deal even without the US. Such a package could help the Iranians justify remaining in the deal, he noted. This could include guaranteeing that Iran can sell oil, which would require the involvement of European central banks as they are harder to sanction by the US than smaller private banks. The EU could also provide development aid and loans and develop a partnership on energy with Iran. "If they were presented to Iran as part of the package the total weight of which is more than the sum of its elements, I think the Iranians would at least have something to consider," Vaez said.