Trump made the harsh comments at the start of a meeting with his French counterpart, Emmanuel Macron, who is in Washington this week to convince the U.S. president not to withdraw from the international, multi-party agreement next month.
"I think we really had some substantive talks on Iran. And we're looking forward to doing something," Trump told reporters after the meeting at the White House with Macron. "We could have at least an agreement among ourselves very quickly. I think we're fairly close to understanding each other."
After the talks, Macron announced that he believes discussions with Trump make it possible to forge a new agreement on Iran, and that he wants the U.S. and France to commit to finding a deal on the agreement.
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Macron said that the deal should not be torn apart but rather added to. He said he can understand Trump's concerns and criticisms.
Trump said other countries in the region should "step up and pay" for what is happening in the Middle East by putting troops on the ground. He still said he wants a new deal on Iran with "solid foundations" and that if Iran threatens the U.S. in any way, it will pay "a price like few countries have ever paid."
Trump has to make a decision on whether or not to remain part of the deal by May 12, and he has signaled that unless significant changes are made to the terms of the agreement, the U.S. will pull out of the deal entirely.
An American withdrawal could lead to the collapse of the entire agreement, and could create a wedge between the U.S. and its European allies.
Macron said earlier this week that there is "no Plan B" to the agreement signed in 2015.
Macron, together with British Prime Minister Theresa May and German Chancellor Angela Merkel — who is due to meet Trump in Washington later this week— has been warning Trump that scrapping the deal could lead to a military crisis in the Middle East, as Iran might use the deal's collapse as an excuse for restarting its military nuclear program, thus "racing" toward the development of a nuclear bomb.
Trump, for his part, stressed the need to keep an eye on Iran for the sake of security in the Middle East. "It just seems that no matter where you go especially in the Middle East, Iran is behind it," he said.
"Wherever there’s trouble, Yemen, Syria, no matter where you have it, Iran is behind it. And now unfortunately, Russia is getting more and more involved. But Iran seems behind everything where there’s a problem. And we just have to take a look," Trump said.
He added, however, that his criticism of the nuclear deal is based on issues the agreement doesn't include. "They're testing missiles," Trump said. "What kind of a deal is it when you don’t talk about Yemen and you don’t talk about all the other problems that we have with respect to Iran?"
When asked about the prospect that Iran may restart its nuclear program if the deal collapsed, Trump said: "it won’t be so easy for them to restart it. They’re not going to be restarting anything. If they restart it, they’re going to have big problems, bigger than they ever had before. And you can mark it down. If they restart their nuclear program they will have bigger problems than they ever had before.”
As Macron headed to the U.S., the Iranian government urged EU leaders to convince Trump not to tear up the 2015 deal between Tehran and six world powers.
Iranian Foreign Minister Mohammad Javad Zarif called on European leaders to support the agreement.
"It is either all or nothing. European leaders should encourage Trump not just to stay in the nuclear deal, but more important to begin implementing his part of the bargain in good faith," Zarif wrote on Twitter.
Speaking to The Associated Press, Zarif said that if President Donald Trump withdraws, Iran would "most likely" abandon the deal as well, and that Iran would no longer be bound by the deal's international obligations.
Iranian President Hassan Rohani on Tuesday warned Trump to remain in the nuclear deal Tehran signed with world powers in 2015, or else he would "face severe consequences."
Minutes after Macron touched down in the United States, the White House said it had no announcements on the Iran deal.
"The president has been extremely clear that he thinks it's a bad deal. That certainly has not changed," White House spokeswoman Sarah Sanders said.
Macron said on "Fox News Sunday" it would be better to protect the deal instead of getting rid of it. "Is this agreement perfect and this JCPOA a perfect thing for our relationship with Iran? No. But for nuclear, what do you have as a better option? I don't see it," he said, referring to the official name of the Iran deal, the Joint Comprehensive Plan of Action.
Reuters contributed background to this report