PARIS (Reuters) - The threat of U.S. sanctions on European companies trading with Iran and tariffs on aluminum and steel exports are a test of European sovereignty and will require a firm response, an adviser to French President Emmanuel Macron said on Monday.

The United States threatened on Sunday to impose sanctions on European companies that do business with Iran, as the remaining participants in the Iran nuclear accord stiffened their resolve to keep that agreement operational.

“It’s an important test of sovereignty,” the French presidential adviser told reporters in a briefing on Monday. “There must really be a software update on these issues of European assertiveness.”

The adviser said French and EU officials were working on different technical and legal issues to preserve existing business ties and financial channels with Iran, and to shield their companies from sanctions.

An update of the 1996 EU legislation against US sanctions, called a blocking statute, was being considered, he said, adding that French and German companies in particular were above all asking for visibility on the subject.

Macron will use the opportunity of an informal EU summit in Sofia, Bulgaria, on Wednesday and Thursday to reaffirm a firm stance on the issue with his EU counterparts.

“There is no sign of division among Europeans,” the adviser said. “Everything indicates that the European position will be firm and united,” he added.

Asked about the possibility of negotiating a new free-trade agreement with the U.S. to avoid the imposition of tariffs on EU aluminum and steel exports, the adviser said President Donald Trump should waive tariffs beyond the current June 1 deadline before any talks can start.

“All Europeans are very clear that, before considering any option of this nature, Americans must offer a permanent and unconditional exemption” to Europe, the official said.

“There is very strong U.S. pressure on this, which requires a firm European response, that’s what the president will say,” he added.

“We can’t negotiate under pressure, with a gun to our head.”