By Robin Emmott and Gabriela Baczynska

LUXEMBOURG (Reuters) – The European Union on Monday reaffirmed its support for a 2015 nuclear deal between Iran and world powers despite sharp criticism of the accord by President Donald Trump, and it urged U.S. lawmakers not to reimpose sanctions on Tehran.

Trump defied both U.S. allies and adversaries on Friday by refusing to formally certify that Tehran is complying with the accord, even though international inspectors say it is, and said he might ultimately terminate the agreement.

EU foreign ministers meeting in Luxembourg said a failure to uphold an international agreement backed by the U.N. Security Council could have serious consequences for regional peace, and also undermine efforts to check North Korea’s nuclear ambitions.

“As Europeans together, we are very worried that the decision of the U.S. president could lead us back into military confrontation with Iran,” German Foreign Minister Sigmar Gabriel told reporters.

After a closed-door meeting chaired by EU foreign policy chief Federica Mogherini on Iran, the ministers issued a joint statement saying the 2015 deal was key to preventing the global spread of nuclear weapons.

“The EU is committed to the continued full and effective implementation of all parts of the JCPOA,” it said, referring to the Joint Comprehensive Plan of Action, the formal name of the accord with Iran agreed in July 2015 in Vienna.

Trump meanwhile renewed his criticism of the accord, and raised the possibility he might try to end it completely.

“We’ll see what phase two is. Phase two might be positive, and it might be very negative. It might be a total termination. That’s a very real possibility. Some would say that’s a great possibility,” the U.S. president said in Washington. He repeated his contention that the JCPOA was “a horrible deal for the United States.”

EU foreign ministers said the accord was crucial to opening up Iran’s $400-billion economy and finding a new market for European investors. Unlike the United States, the EU saw relations with Iran flourish in the late 1990s until revelations about Tehran’s nuclear plans in 2002.

“Non-proliferation is a major element of world security and rupturing that would be extremely damaging,” French Foreign Minister Jean-Yves Le Drian told reporters. “We hope that Congress does not put this accord in jeopardy.”

Mogherini said she would travel to Washington early next month to try to muster support for the accord.

The International Atomic Energy Agency (IAEA) says Iran is complying with its commitments under the accord, which Trump has branded “the worst deal ever negotiated”.

The EU still has sanctions in place against members of Iran’s Islamic Revolutionary Guard Corps, a major target of Trump’s criticism.

The EU ministers also discussed on Monday Iran’s ballistic missile program, which they want to see dismantled. Tehran says that program is purely defensive.

NORTH KOREA SPILLOVER

Negotiated after 12 years of talks, the accord with Iran is the most significant diplomatic success for the bloc in several decades.

Many worry that the EU’s reputation as an honest broker in a host of future conflicts may not recover if the U.S. Congress reimposes sanctions on Iran and causes the deal – which had the strong backing of Trump’s predecessor Barack Obama – to unravel.

Most U.N. and Western sanctions were lifted more than 18 months ago under the deal, though Tehran is still subject to a U.N. arms embargo, which is not part of the deal.

EU foreign ministers also approved a new batch of economic sanctions on North Korea after its atomic test last month that included an oil embargo and investment ban.

But some still hold out hope of repeating the Iran nuclear deal with Pyongyang at some future date.

Sweden is one of only seven EU countries with an embassy in Pyongyang and its foreign minister, Margot Wallstrom, reiterated that Stockholm could be counted on to help negotiate if asked.

But Germany’s Gabriel warned that Trump’s decision not to certify the Iran accord could scupper such hopes, a position echoed by Mogherini, although she stressed that no such EU mediation was underway.

“My concern is that, if we want to talk to North Korea now, the possible end for the nuclear deal with Iran would jeopardize the credibility of such treaties,” Gabriel said.

(Additional reporting by Peter Maushagen in Luxembourg, Lily Cusack in Brussels and Roberta Rampton in Washington; Editing by Gareth Jones and Alistair Bell)