German Chancellor Angela Merkel, standing alongside US President Donald Trump at the White House, said Friday that the existing international accord on Iran is not enough to curb the Islamic republic’s nuclear ambitions.

The so-called Joint Comprehensive Plan of Action, signed by Tehran and six world powers including Germany and the United States, is “a first step that has contributed to slowing down their activities in this particular respect,” Merkel told reporters.

“But we also think from a German perspective that this is not sufficient in order to see to it that Iran’s ambitions are curbed and contained.”

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She added: “Europe and the United States ought to be in lock step on this.”

Trump welcomed Merkel to the White House for a visit of less than three hours. The two discussed Trump’s demand for an overhaul by May 12 of the nuclear deal — an agreement that Germany believes should remain in place.

Although Germany is unlikely to accept a wholesale rewrite of the deal, Berlin has indicated that it is prepared to consider add-ons that would crack down on Tehran’s ballistic missile program and curb Iranian efforts to strengthen its strategic role in the Middle East.

US Secretary of State Mike Pompeo said Friday that Trump has not yet decided whether to quit the nuclear deal with Iran, warning that he was unlikely to remain in it if the accord goes unchanged. Pompeo said he and his team were working to see if the president’s concerns could be addressed.

“There has been no decision made,” Pompeo said at a press conference after meeting with NATO foreign ministers in Brussels.

But, he added, “The president has been clear. Absent a substantial fix, absent overcoming the shortcomings, the flaws of the deal, he is unlikely to stay in that deal past this May.”

He also said that he would be discussing ways to address Trump’s concerns during his upcoming trip to the Middle East, during which he will hold high-level talks in Saudi Arabia, Israel and Jordan.

“I am confident that that will be a topic on my trip throughout the Middle East as well, not only talking about the concerns that President Trump has expressed consistently, but talking about ways to potentially address those shortcomings, finding potential solutions to the very flaws that President Trump has identified for a long time now,” he said.

“The team is working and I am sure we will have lots of conversations to deliver” a fix, he said.

Earlier this week, French President Emmanuel Macron made clear that France would not follow the US lead if Trump decides to withdraw from the agreement.

Macron later told French reporters that he has no “inside information” on Trump’s decision on the Iran deal but noted that it’s clear the US president “is not very much eager to defend it.”

US Defense Secretary Jim Mattis on Thursday emphasized the value of certain aspects of the Iran nuclear agreement, even as President Trump considers pulling out.

Without explicitly giving his opinion about whether the United States should stick with the agreement, Mattis said that after reading the full text of the deal three times, he was struck by provisions that allow for international verification of Iran’s compliance. He said that since becoming defense secretary in January 2017, he also has read what he called a classified protocol in the agreement.

“I will say it is written almost with an assumption that Iran would try to cheat,” he said in testimony before the Senate Armed Services Committee. “So the verification, what is in there, is actually pretty robust as far as our intrusive ability to get in” with representatives of the International Atomic Energy Agency to check on compliance.

“Whether that is sufficient I think is a valid question,” he said, after Sen. Dan Sullivan, R-Alaska, said the nuclear deal was not supported by Congress. The committee’s senior Democrat, Sen. Jack Reed of Rhode Island, told Mattis the Iran deal is “working as intended” and that withdrawing would ease Iran’s path to nuclear weapons.

Mattis said Iran’s history of hiding a nuclear weapons program makes it “suspect,” and he noted his concern about other Iranian activities, including its role in supporting Syria’s president, Bashar Assad, and supplying its proxy forces in Yemen.

The Pentagon chief said the administration was still considering whether the nuclear deal can be improved enough to persuade Trump it is worth preserving. “It’s going on today as we speak,” he said of the consultations. Trump has said he will decide by May 12.

Mattis reiterated his view that the deal is “imperfect” and said “there are obviously aspects of the agreement that can be improved upon.”

The question being discussed within the administration, and between the US and its European allies, he said, is “whether we can repair it enough to stay in it or if the president is going to decide to withdraw from it.” He too said Trump has not yet made a decision.

Mattis in the past has said he believes the agreement is flawed but that the US should stick with it.

Iran’s has repeatedly ruled out any changes or additions to the accord.

The accord required Iran to give up its nuclear ambitions — but leave most of its nuclear infrastructure intact — in exchange for relief from the crippling sanctions that had been imposed on it.

The deal’s critics argue that the “sunset clauses” in the deal, periods of time after which Iran can begin enriching uranium, mean that the country is not actually prevented from developing a nuclear weapon, but is merely delayed. Others argue that international inspectors are not able to freely investigate locations like military facilities, something which may be exploited by Iran in order to violate the deal without getting caught.

In addition, the nuclear deal is narrowly focused and does not address the country’s ballistic missile programs or its support for terrorist groups and dictators across the Middle East.