WASHINGTON (Reuters) - 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.

National security adviser John Bolton arrives for a joint news conference between U.S. President Donald Trump and Germany's Chancellor Angela Merkel in the East Room of the White House in Washington, U.S., April 27, 2018. REUTERS/Kevin Lamarque

White House national security adviser John Bolton said U.S. sanctions on European companies that maintain business dealings with Iran were “possible,” while Secretary of State Mike Pompeo said he remained hopeful Washington and its allies could strike a new nuclear deal with Tehran.

Bolton struck a more hawkish tone with his comments in an interview with CNN’s “State of the Union” program than Pompeo did on “Fox News Sunday.”

U.S. President Donald Trump said on Tuesday that the United States was withdrawing from a 2015 deal negotiated by the Obama administration.

So far, China, France, Russia, Britain, Germany and Iran remain in the accord, which placed controls on Iran’s nuclear program and led to a relaxation of economic sanctions against Iran and companies doing business there.

Despite the U.S. exit, Britain and Iran expressed their commitment on Sunday to ensuring that the accord is upheld, according to a statement released by British Prime Minister Theresa May’s office.

French Foreign Minister Jean-Yves Le Drian, speaking in Dublin, declared: “We are stakeholders” and will remain so.

Germany said it would spend the next few months trying to persuade Washington to change its mind. German Foreign Minister Heiko Maas acknowledged, however, that protecting European companies from potential U.S. penalties could be difficult.

Asked whether the United States might impose sanctions on European companies that continue to do business with Iran, Bolton told CNN: “It’s possible. It depends on the conduct of other governments.”

Pompeo said he was “hopeful in the days and weeks ahead we can come up with a deal that really works, that really protects the world from Iranian bad behavior, not just their nuclear program, but their missiles and their malign behavior as well.”

The White House said Trump had spoken with French President Emmanuel Macron on Saturday and “reiterated the need for a comprehensive deal that addresses all aspects of Iran’s destabilizing activity in the Middle East.”

In a tweet on Sunday, Trump wrote: “Remember how badly Iran was behaving with the Iran Deal in place. They were trying to take over the Middle East by whatever means necessary. Now, that will not happen!”

TRYING ‘TO PERSUADE’ U.S.

The U.S. withdrawal from the Iran deal has upset Washington’s European allies, cast uncertainty over global oil supplies and raised the risk of conflict in the Middle East.

Germany’s minister for economic affairs, Peter Altmaier, said on Sunday that Berlin would try to “persuade the U.S. government to change its behavior.”

In an interview with ZDF public television, Altmaier noted the United States had set a 90-day deadline for foreign firms to comply with the return of sanctions and that this period could be used to convince Washington to change course.

Israel and Iran engaged in an extensive military exchange on the heels of Trump’s decision to leave the deal. Macron told Trump in their telephone call on Saturday that he was worried about stability in the Middle East, according to Macron’s office.

As a private citizen, Bolton suggested in the past that the United States push for a change in Iran’s government. But in an interview on ABC’s “This Week” program, Bolton said: “That’s not the policy of the administration. The policy of the administration is to make sure that Iran never gets close to deliverable nuclear weapons.” [L2N1SK088]

In the CNN interview, Bolton did not respond directly when asked whether Trump might seek “regime change” in Iran, or whether the U.S. military would be ordered to make a pre-emptive strike against any Iranian nuclear facility.

“I’m not the national security decision-maker,” Bolton said, adding that Trump “makes the decision and the advice that I give him is between us.”

Bolton said Europe was still digesting Trump’s move last week.

“I think at the moment there’s some feeling in Europe - they’re really surprised we got out of it, really surprised at the reimposition of strict sanctions. I think that will sink in; we’ll see what happens then,” Bolton said.