EU countries on Monday gave European firms legal cover to operate in Iran despite the US pullout from the nuclear deal, after a report that the Trump administration has rejected calls by Brussels for an exemption from sanctions.
The bloc's foreign policy chief Federica Mogherini said the 28 countries were doing all they could to save the deal but conceded President Donald Trump's administration could still wreck it.
"Today, the (European) Council has endorsed the update of the blocking statute annex on the nuclear deal with Iran," Mogherini told reporters in Brussels at a meeting with EU foreign ministers.
She said the European Parliament gave its consent to the statute two weeks ago.
The "blocking statute" forbids EU firms from complying with US sanctions, allowing them to recover damages from such penalties and nullifying any foreign court rulings against them.
The blocking statute is due to enter force on August 6, when the first set of US sanctions are due. The second set is due November 4, just before US legislative elections.
Mogherini conceded it will be tough battle to preserve the Iran nuclear agreement, which Trump's predecessor Barack Obama sealed with Iran along with Britain, France and Germany as well as Russia and China.
"It is a difficult exercise, because the weight of the US in the global economy and the financial system is obviously relevant," the former Italian foreign minister said.
Mogherini said the EU and other parties were "determined to preserve this deal" she called vital to European, Middle Eastern and global security.
"We will continue to do all we can to try and prevent this deal from being dismantled because we believe the consequences of this would be catastrophic for all." But she added she was not sure the "efforts are going to be enough."