WASHINGTON: The US unleashed its "toughest ever" sanctions against Tehran on Monday, while a defiant Iranian President Hassan Rouhani vowed to continue selling its crude oil in the international market despite the measures. "We should break the sanctions very well and we will do that," Rouhani said shortly after the anti-Iran sanctions took effect.

US President Donald Trump's administration reinstated all sanctions lifted under the 2015 nuclear deal, targeting both Iran and countries that trade with it, the BBC reported. Tehran had struck the nuclear deal with six world powers and the EU, agreeing to curb its nuclear programme in return for the lifting of restrictions mainly on its oil sales.

Accusing Iran of stirring up regional instability and exporting violence, Washington terminated the nuclear accord on May 8 and said called it "one of the worst and most one-sided deals the US had ever entered into".

More than 700 individuals, entities, vessels and aircraft were now on the sanctions list, including major banks, oil exporters and shipping companies. The measures will make it difficult to do business with the oil-rich nation.

Washington said that it wanted to stop what it calls Tehran's "malign" activities including cyber attacks, ballistic missile tests and support for terror groups and militias in the Middle East.

The Trump administration, meanwhile, granted exemptions to eight countries to continue importing Iranian oil, without naming them. They reportedly include US allies India, Italy, Japan and South Korea.

"With the help of the people and the unity that exists in our society, we have to make the Americans understand that they must not use the language of force, pressure and threats to speak to the great Iranian nation. They must be punished once and for all," Rouhani said at a meeting of economic officials.

"The US officials have come to the understanding that they could not replace the Iranian oil on the market," he said, adding that even if they did not grant waivers to some countries to keep trading oil with Iran, "we would still be able to sell our oil and we have adequate capabilities to do that".

Rouhani said Europe, too, was angry at the US policies, Press TV reported.

"Today, we are not the only ones who are angry at US policies; even European businesses and governments are angered by US policies, too."

Rouhani also said he believed that America had never before seen as lawless an administration as that of Trump's.

He said all US administrations had violated international law, but "these (current officials) score on top on the lawlessness rankings".

"I don't recall a group assuming power at the White House that was racist as these."

The Iranian military said it would hold air defence drills to prove Tehran's capabilities.

Before travelling to a campaign rally for the US midterm elections, Trump said Iran was already struggling under his administration's policies.

"The Iran sanctions are very strong. They are the strongest sanctions we've ever imposed. And we'll see what happens with Iran, but they're not doing very well, I can tell you."

The UK, Germany and France -- which were among the five countries still committed to the nuclear pact -- objected to the sanctions.

They promised to support European firms that do "legitimate business" with Iran and set up an alternative payment mechanism that will help companies trade without facing US penalties.

On Sunday, thousands of Iranians chanting "Death to America" rallied, rejecting calls for talks. The rallies coincided with the siege of the US Embassy on November 4, 1979.

A total of 52 Americans were held hostage in the Embassy for 444 days and the two countries have been enemies ever since.