WASHINGTON - U.S. President Donald Trump warned Iran Wednesday there would be "very severe consequences" if it starts developing nuclear weapons in the wake of the U.S. withdrawal from a 2015 international pact aimed at restraining Tehran's nuclear program.
In brief comments at the White House, Trump said the United States would "very shortly" reimpose economic sanctions in an attempt to force Iran to negotiate new terms on the deal, its ballistic missile tests and military advances in Syria, Yemen and elsewhere in the Middle East.
WATCH: Trump Says Iran Will Agree to Negotiate on Nuclear Deal
The U.S. leader accused Iran of creating "bedlam and death" in the region.
"We're going to make a very good deal or we won't make a deal at all," he said. Trump acknowledged the U.S. "probably won't do very well with them," but said that was all right with him.
Trump continued to assail the nuclear pact Tehran reached with the U.S. under his predecessor, Barack Obama, calling it a "terrible, terrible deal that should never have been done."
Trump's comments came as the other five signatories to the accord -- Germany, Britain, France, Russia and China -- all voiced renewed support for the deal.
French President Emmanuel Macron spoke to Iranian President Hassan Rouhani by phone Wednesday for more than an hour. Macron's office said the French president told his Iranian counterpart that he wants to continue the accord "in all its dimensions." The French presidency said Rouhani expressed the wish to "do everything to stay in the deal."
German Chancellor Angela Merkel called the U.S. withdrawal from the 2015 accord regrettable and said Berlin would "try to do everything so that Iran also fulfills its commitments in the future."
She said Trump's abandonment of the deal "showed us once again that we will face more responsibility in Europe, in foreign policy, in the area of securing peace, in the area of the political solutions we must find."
British Foreign Secretary Boris Johnson urged the U.S. "to avoid taking any action that would hinder other parties from continuing to make the agreement work," saying the deal was "vital" to Britain's national security.
Johnson said it falls to the U.S. administration to "spell out their view of the way ahead."
The Kremlin said Russian President Vladimir Putin expressed "deep concern over [Trump's] decision and once more stressed the importance of this document," while France and China also voiced continued support.
Trump said the agreement "didn't bring calm, it didn't bring peace, and it never will."
Defense Secretary Jim Mattis told a congressional hearing Wednesday that the U.S. "will continue to work alongside our allies and partners to ensure that Iran can never acquire a nuclear weapon, and will work with others to address the range of Iran’s malign influence. This administration remains committed to putting the safety, interests, and well-being of our citizens first."
In a new assessment, however, the head of the United Nations nuclear watchdog unit, the International Atomic Energy Agency, said, "As of today, the IAEA can confirm that the nuclear-related commitments are being implemented by Iran."
Middle East reacts
Trump won praise from Israeli Prime Minister Benjamin Netanyahu, who has long derided the pact as woefully insufficient in blocking Iran from developing a nuclear weapon.
Trump also won some support in the Arab world for his withdrawal from the deal. The United Arab Emirates, Bahrain and Saudi Arabia all voiced their approval of Trump's action.
Iran's Supreme Leader, Ayatollah Ali Khamenei, challenged Trump's withdrawal from the agreement, saying, "You cannot do a damn thing!" Without elaborating, he claimed Trump had "over 10 lies" in announcing the U.S. was pulling out of the accord.
The head of Iran's Revolutionary Guard, General Mohammad Ali Jafari, said the decision showed the U.S. was "not trustworthy."
Andrew Peek, a deputy U.S. assistant secretary of state for Iraq and Iran, told CNN the Trump administration believes that by withdrawing from the nuclear pact, the U.S. can "frankly get better comprehensive control" over Iran's ballistic missile tests and military advances in Syria, Yemen and elsewhere in the Middle East through new negotiations with Iran.
"Iran's behavior across the spectrum concerns me every day," Peek said.
He said the U.S. has "every confidence" that economic sanctions the U.S. plans to reimpose on Iran will force the Islamic Republic to restart negotiations over its nuclear program and other military issues.