Iran accused the United States on Thursday of "childish behaviour" driven by fear after Washington imposed sanctions on its foreign minister, escalating tensions between two foes at loggerheads over Gulf shipping and Iran's nuclear programme.
The European Union meanwhile said Thursday it regrets the US decision to impose sanctions against Iran's foreign minister Mohammad Javad Zarif and vowed to continue working with him.
"We regret this decision," said Carlos Martin Ruiz De Gordejuela, a spokesman for EU diplomatic chief Federica Mogherini.
"From our side, we will continue to work with Mr Zarif as Iran's most senior diplomat and in view of the importance of maintaining diplomatic channels," Martin said.
The decision Wednesday was the latest blow by President Donald Trump to the 2015 international deal to curb Iran's nuclear programme, which Brussels has been trying to salvage.
Fears of a Middle East war with global repercussions have risen since the United States pulled out of the deal signed with Iran under Donald Trump's predecessor Barack Obama. The Trump administration has since revived sanctions on Tehran.
The Islamic Republic has retaliated by resuming uranium enrichment seen in the West seen as a potential conduit to developing atomic bombs. Iran denies any such intent.
After several attacks on tankers - blamed by Washington on Tehran, which denied responsibility - the United States is trying to forge a coalition to secure Gulf waters, though European allies have been loath to join for fear of provoking open conflict.
European parties to the nuclear pact have called for diplomacy to defuse the crisis, but Tehran and Washington have taken hard lines and on Wednesday the Trump administration slapped sanctions on Iran's foreign minister in a likely further blow to any chances for troubleshooting dialogue.
"They (Americans) are resorting to childish behaviour... They were claiming every day 'We want to talk, with no preconditions' ...and then they sanction the foreign minister," Iranian President Hassan Rouhani said on state television.
Zarif, a pivotal player in the nuclear deal who was educated and lived for years in the United States, dismissed the action and said it would not affect him as he had no property or other interests in America.
Iran says US afraid
"A country which believes it's powerful and a world superpower is afraid of our foreign minister's interviews," Rouhani said, alluding to numerous interviews that Zarif - a fluent English speaker - gave to American media when he visited New York for a United Nations conference in July.
"When Dr Zarif gives an interview in New York, ... they (Americans) say Iran's foreign minister is misleading our public opinion," Rouhani said. "What happened to your claims of liberty, freedom of expression and democracy?"
Rouhani added: "The pillars of the White House are made to tremble by the words and the logic of a knowledgeable and self-sacrificing man and diplomat."
US Treasury Secretary Steven Mnuchin said Zarif was being sanctioned because he "implements the reckless agenda of Iran's Supreme Leader...(We are) sending a clear message to the Iranian regime that its recent behaviour is completely unacceptable".
In a tweet earlier on Thursday, Zarif said peace and dialogue were an "existential threat" to hawkish politicians allied with US President Donald Trump who take a hardline stance against the Islamic Republic including including Trump's national security adviser John Bolton, an ardent Iran hawk, and conservative Israeli Prime Minister Benjamin Netanyahu.
In repudiating the nuclear deal reached by predecessor Barack Obama, Trump said he wanted to secure a wider accord that not only limited Iran's nuclear activity but also curbed its ballistic missile programme and reined in its support for powerful proxies in Syria, Iraq, Yemen and Lebanon.
Trump intensified sanctions in May to try to strangle Iran's oil exports, the lynchpin of its economy.
The security of shipping in the Gulf, through which about a fifth of the world's oil passes, has shot up the international agenda since May when Washington accused Iran of being behind explosions that holed six tankers over several weeks.
In July, Iran seized a British-flagged tanker in the Strait of Hormuz, the Gulf's outlet to the open seas, in apparent retaliation for Britain's seizure of an Iranian ship accused of violating European sanctions by taking oil to Syria.
In a sign of increasing jitters over security in the Gulf, Royal Dutch Shell said on Thursday it was not taking any British-flagged tankers through the Strait of Hormuz for the time being.
The US Embassy in Berlin said on Tuesday the United States had asked Germany to join France and Britain in a mission to protect shipping transiting the strait and "combat Iranian aggression". Germany rebuffed the request.
"Germany will not take part in the sea mission presented and planned by the United States," Foreign Minister Heiko Maas said. The Gulf situation was serious and everything should be done to avoid conflict, he said. "There is no military solution."
"To join the American position, which in our view is part of a strategy of maximum pressure, has never been the right path for us and will not be in the future," Maas told Germany's ZDF television.
On Thursday, Richard Grenell, US ambassador to Germany, urged Berlin to take on a global responsibility to match its economic might. "Germany is the biggest economic power in Europe. This success brings global responsibilities," he said.
The foreign ministry of Russia, another party to the 2015 deal, said it had the impression the United States was seeking a pretext for conflict in the Gulf, RIA news agency reported.