The US on Monday imposed "the toughest ever" sanctions on a defiant Iran aimed at altering the Iranian regime's "behaviour", even as the Trump administration dodged a question whether it has got firm commitments from India and China to stop all oil purchases from Tehran within six months.

The sanctions cover Iran's banking and energy sectors and reinstate penalties for countries and companies in Europe, Asia and elsewhere that do not halt Iranian oil imports.

The sanctions follow US President Donald Trump's controversial decision in May to abandon the 2015 multi-nation nuclear deal with Tehran.

President Trump says that he wants to get Iran back to the negotiating table on the nuclear issue. The Trump administration also says it wants to stop what it calls Tehran's "malign" activities including cyber attacks, ballistic missile tests, and support for terror groups in the Middle East

India and China -- the two biggest buyers of Iranian crude, have so far appeared to have skipped the punitive American sanctions targeting the Iranian oil and financial sectors.

The two Asian giants are believed to be among the eight countries that have been given the rare temporary exemptions from the Iranian sanctions that kicked off on Monday.

The Trump administration said it has asked these countries including Turkey, Iraq, Italy, Japan and South Korea to bring down their oil purchase to zero as soon as possible.

US Secretary of State Mike Pompeo, during a talk show on Fox News, refused to reveal which countries received waivers from US sanctions to continue importing Iranian oil.

But he said the eight unidentified nations "need a little bit more time to get to zero."

He repeatedly parried questions when asked about the commitment from India and China on zero-oil purchase from Iran.

"Watch what we do. Watch as we've already taken more crude oil off the market than any time in previous history. Watch the efforts that President Trump's policies have achieved. We've done all of this, too, while making sure that American consumers don't suffer, he said, as he avoided giving a direct answer on India and China.

I am very confident that the sanctions that will be re-imposed this Monday, not only the crude oil sanctions, that the financial sanctions that are being put in place by the Treasury Department and over 600 designations of individuals and companies in Iran will have the intended effect to alter the Iranian regime's behaviour. That's our expectation. It's the reason for President Trump's policy, he asserted.

India, which is the second biggest purchaser of Iranian oil after China, is willing to restrict its monthly purchase to 1.25 million tonnes or 15 million tonnes in a year (300,000 barrels per day), down from 22.6 million tonnes (452,000 barrels per day) bought in 2017-18 financial year, sources in New Delhi had said last week.

The reimposition of US sanctions on Iran, Pompeo asserted are "the toughest ever" on Tehran.

They're aimed at a singular purpose, denying the world's largest state sponsor of terrorists the capacity to do things like they did this past couple weeks, attempted assassination campaign in the heart of Europe, he said.

These sanctions have already had an enormous impact. We've already reduced Iranian crude oil experts by over a million barrels per day. That number will fall farther. There's a handful of places were countries that have already made significant reductions in their crude oil exports need a little bit more time to get to zero, and we're going to provide that to them, he said.

The State Department did not respond to a PTI question as to what will happen if India does not bring down its oil purchase from Iran to zero, as being demanded by it, in next six months.

It also did not respond to a question on the fate of the the strategically crucial Iranian port of Chabahar, which India sees as critical for reaching landlocked Afghanistan and Central Asia.

Trump told reporters on Sunday that the sanctions are the strongest ever imposed by the US.

The Iran sanctions are very strong. They're the strongest sanctions we've ever imposed. We'll see what happens with Iran, but they're not doing very well, I can tell you, Trump told reporters at the White House. The president did not respond to a question about the waiver.

At an election rally on Sunday, Trump said the Iranian regime now just want to survive.

I withdrew the United States from the horrible, one-sided Iran nuclear catastrophe. And Iran is a much different right now than it was before I took office, Trump said at an election rally in Chattanooga in Tennessee.

They were doing bad things, and they are doing bad things now, but they don't have the same perspective. They were looking for the Mediterranean. .. They wanted to take over the whole Middle East. Right now, they just want to survive, Trump said.

In May, President Trump had pulled US out of the 2015 Joint Comprehensive Plan of Action (JCPOA) terming it as disastrous. Under the Obama-era deal, involving five permanent members of the UN Security Council and Germany, Iran agreed to stop its nuclear programme in exchange for relief from economic sanctions.

President Hassan Rouhani on Monday said Iran "will proudly bypass sanctions" by the US.

"We are in a situation of economic war, confronting a bullying power. I don't think that in the history of America, someone has entered the White House who is so against law and international conventions," he added.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)