Iranian President Hassan Rouhani vowed to continue his efforts to end the country's isolation as he was sworn in for a second term, a day after US President Donald Trump signed a bill increasing sanctions against the Islamic Republic.

"We will never accept isolation," Rouhani told a packed audience of Iranian political and military officials in Tehran on Thursday.

"The nuclear deal is a sign of Iran's goodwill on the international stage," he said, referring to the 2015 agreement to curb its atomic programme in exchange for an easing of sanctions.

The US agreed the deal with world powers including Russia, Britain, France, China and Germany.

Rouhani, a 68-year-old moderate who has faced fierce criticism from conservatives for his efforts to rebuild ties with the West, issued a call for unity.

"I declare once again that with the election concluded, the time for unity and cooperation has begun," he said.

"I extend my hand to all those who seek the greatness of the country."

Trump, who during his election campaign last year called 2015’s nuclear agreement "the worst deal ever", signed new sanctions into law on Wednesday, along with measures against Russia and North Korea.

The agreement had been negotiated by the administration of Barack Obama, former US president.

'Nuclear deal violated'

Iran had already said it would complain to the body that oversees the deal about the new measures, which were passed in Congress last week in response to an alleged missile development programme and human rights abuses.

An Iranian official said on Tuesday that the new US sanctions break the terms of the nuclear deal.

"In our view the nuclear deal has been violated and we will show an appropriate and proportional reaction to this issue," Deputy Foreign Minister Abbas Araqchi said in an interview with state TV, according to the ISNA news agency.

While Russia has reacted to the sanctions by ejecting US embassy staff, Iran has no diplomatic relations or direct trade links with the US so its retaliation options are limited.

Araqchi said Tehran's response would be "intelligent".

"The main goal of America in approving these sanctions against Iran is to destroy the nuclear deal and we will show a very intelligent reaction to this action," Araqchi said. "We are definitely not going to act in a way that get us entangled in the politics of the American government and Trump."

The move by Trump is likely to embolden his hardline critics, who say the nuclear deal was a form of capitulation.

"If the sanctions are to be implemented, there will be problematic times for Iran and for the nuclear deal in general," Hassan Ahmadian, a professor at the University of Tehran, told Al Jazeera. "Now in Iran, there is a growing debate if these sanctions violate [the nuclear deal] or not.

"And the second debate is, if these sanctions are to be implemented, how should Iran respond?"

Sanctions targeting individuals

The US legislation imposes mandatory penalties on people involved in Iran's ballistic missile programme.

It would also apply sanctions to Iran's Revolutionary Guard and enforce an arms embargo.

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The deal has seen European countries flocking back to invest in oil-rich Iran, with the French energy giant Total agreeing to develop a new phase of the South Pars natural gas field, the world's largest.

Araqchi said the Europeans would not allow Trump to destroy the nuclear deal.

"What Total did and the contract that was signed between this company and Iran sent a message from Europe to the Americans that whatever the conditions they will continue their economic relations with Iran," he said.

Ellie Geranmayeh, an Iran analyst with the European Council on Foreign Relations, said the timing of the new US sanctions package was "unfortunate".

"What will be absolutely critical is how the Europeans position themselves," she said, pointing to the burgeoning trade ties with Europe and their continued backing of the nuclear deal.