The European Union on Thursday urged Iran to respect the international agreement curbing the Islamic Republic’s nuclear ambitions, and added that the bloc aims to continue trading with the country despite US sanctions.

The EU and major European powers — Britain, France and Germany — also said that they “note with great concern the statement made by Iran concerning its commitments” to the nuclear deal, stressing that they “reject any ultimatums” coming from Tehran.

The joint statement came as the bloc struggles to preserve the 2015 nuclear deal with Iran, a day after a new deadline from Tehran on finding a solution to make up for last year’s unilateral US withdrawal from the accord and re-imposed US sanctions on Iran.

“We remain fully committed to the preservation and full implementation” of the deal, endorsed by the U.N. Security Council, said the EU statement.

The Trump administration pulled America out of the 2015 deal a year ago, saying it does nothing to stop Iran from developing missiles or destabilising the Middle East. The Europeans insist that the pact is an important pillar of regional and global security and was never meant to address those other issues.

United States President Donald Trump has tightened the screws further on Iran with sanctions on its mining industry after a frustrated Tehran said it would suspend some promises it made under a nuclear deal rejected by Washington.

On the anniversary of Trump's withdrawal from the accord he denounced as "horrible", tensions were soaring as the US deployed an aircraft carrier strike group and nuclear-capable bombers to the region and accused Iran of “imminent” attacks.

In an announcement previewed for days, Iran said it would immediately stop implementing some restrictions under the 2015 deal — a move aimed largely at pressing Washington's European allies to step up to preserve the agreement.

Tehran said it would abandon even more if the remaining parties to the agreement — Britain, China, France, Germany and Russia — failed to start delivering on their commitments to sanctions relief within 60 days.

Iranian President Hassan Rouhani said the ultimatum was intended to rescue the nuclear deal from Trump, whose sanctions have caused severe pain in Iran, which had anticipated an economic boon from the agreement negotiated under then-president Barack Obama.

“We felt the [deal] needed surgery and that the year-long sedatives have not delivered any result. This surgery is meant to save the [deal], not destroy it,” Rouhani said at a cabinet meeting broadcast live on state television.

Rouhani denounced European countries for seeing the US as the world's “sheriff” and said their view kept them from making “firm decisions for their own national interests".

“Iran must remain in this agreement and we must do everything we can to ensure that it stays in,” French President Emmanuel Macron told reporters at an EU summit on Thursday in Romania, where leaders were to discuss the standoff.

Amid the heated rhetoric from Tehran and Washington, Macron urged the agreement’s signatories not to “get caught up in any escalation” and to “jointly watch over our collective security”.

In their statement, the EU powers said they “regret the re-imposition of sanctions” by the US and remain “determined to continue pursuing efforts to enable the continuation of legitimate trade with Iran".

The Europeans have set up a complicated barter-type system to skirt direct financial transactions with Iran and so evade possible US sanctions. The workaround, dubbed INSTEX, is not yet operational as Iran has not completed its part of the scheme.

The bloc said it plans to push ahead with “the operationalization of the special purpose vehicle ‘INSTEX’".

In a message implicitly directed at the US administration, the EU powers said “we call on countries not party to the (deal) to refrain from taking any actions that impede the remaining parties’ ability to fully perform their commitments”.

Cutting Iranian exports

Trump quickly fired back on Wednesday as he moved to inflict greater economic pain on Iran, imposing sanctions that would punish anyone who buys or trades the country's iron, steel, aluminium and copper.

The White House had already acted forcefully to prevent all countries from buying Iran's oil — its crucial money-maker — and said that the steel and mining sector was the country's second-largest source of foreign revenue, accounting for 10 per cent of exports.

“Tehran can expect further actions unless it fundamentally alters its conduct,” Trump said in a statement.

But in a shift in tone, Trump — who talked tough on North Korea before two landmark summits with leader Kim Jong Un — said he was willing to negotiate face-to-face.

“I look forward to someday meeting with the leaders of Iran in order to work out an agreement and, very importantly, taking steps to give Iran the future it deserves,” he said.

At a rally in Florida late on Wednesday, Trump said he hopes that “a fair deal” can be worked out at some point.

“We aren't looking to hurt anybody,” he told supporters. “We just don't want them to have nuclear weapons. That's all we want.”

Observers believe it is highly unlikely that Iran's leaders — who have made hostility to the US a bedrock principle since the 1979 Islamic Revolution toppled the pro-Western shah — would want to meet Trump, who has repeatedly threatened the country.

But Iranian Foreign Minister Mohammad Javad Zarif regularly saw his counterpart in the Obama administration, then secretary of state John Kerry, and recently dangled the prospect of a prisoner swap with the US.

Moving limits on uranium, heavy water

Iran's Supreme National Security Council said it no longer considered itself bound by the agreed restrictions on stocks of enriched uranium and heavy water.

It said that after 60 days, it would also stop abiding by limits on the level to which Iran can enrich uranium and modifications to its Arak heavy water reactor that were designed to prevent the production of plutonium.

Uranium enriched to much higher levels than Iran's current stocks can be used as the fissile core of a nuclear weapon, while heavy water is a source of plutonium, which can be used as an alternative way to produce a warhead.

Robert Kelley, a former United Nations nuclear inspector now with the Stockholm International Peace Research Institute, said on a practical level, the commitments Iran was dropping had no bearing on its ability to develop an atomic bomb.

He added that Iran was simply seeking to “save face” after “striking a deal which was not respected by the other side".