Iran, Russia and European leaders roundly condemned President Trump’s decision on Friday to disavow the Iran nuclear deal, saying that it reflected the growing isolation of the United States, threatened to destabilize the Middle East and could make it harder to resolve the growing tensions on the Korean Peninsula.

The reaction was far from panicked, as Mr. Trump’s decision punts to Congress the critical decision of whether the United States will reimpose sanctions on Iran — a step that would effectively sink the deal.

But Mr. Trump also warned that unless the nuclear agreement was altered and made permanent — to prohibit Iran from ever developing nuclear weapons — he would terminate the agreement, an ultimatum that threw the future of the accord into question.

Though they avoided direct criticism of Mr. Trump, Prime Minister Theresa May of Britain, Chancellor Angela Merkel of Germany and President Emmanuel Macron of France said in a rare joint statement that they “stand committed” to the 2015 nuclear deal and that preserving it was “in our shared national security interest.”

“The nuclear deal was the culmination of 13 years of diplomacy and was a major step towards ensuring that Iran’s nuclear program is not diverted for military purposes,” they added.

Sigmar Gabriel, Germany’s foreign minister, said that Mr. Trump was sending “a difficult and also from our point of view dangerous signal.”

He said that the Iran deal, and other diplomatic achievements, were necessary “to convince countries like North Korea, and maybe also others, that it is possible to create security without acquiring nuclear weapons.”

“Destroying this agreement would, worldwide, mean that others could no longer rely on such agreements — that’s why it is a danger that goes further than Iran,” he added.

Reaction from Iran was quick and pointed. Appearing on television, its president, Hassan Rouhani, denounced Mr. Trump and called the United States an outlier that had become “more lonely than ever” in the international community. Mr. Rouhani did not threaten to withdraw from the deal, but made it clear that he would not renegotiate the terms, either.

“The statements of Mr. Trump are nothing but abuse and threats against the people of Iran,” he said. “An international agreement cannot be disregarded.”

The European leaders noted that the United Nations Security Council had unanimously endorsed the deal, and that the International Atomic Energy Agency had confirmed Iran’s compliance with it.

But Mr. Trump’s aggressive stance on Iran won plaudits from several nations on Friday, specifically from adversaries of Iran like Israel, Saudi Arabia and the United Arab Emirates.

Benjamin Netanyahu, the Israeli prime minister who has always opposed the agreement with Iran, said that Mr. Trump’s announcement created “an opportunity to fix this bad deal” and was a sign of Mr. Trump’s determination to “boldly confront Iran’s terrorist regime.”

Saudi Arabia, which has waged a proxy battle against Iran for supremacy in the region and was the first country Mr. Trump visited after taking office, said it welcomed what it called a “new U.S. strategy” toward Iran. Continue reading.