It's time for the United States to hold Iran accountable.

Iran's atomic chief has warned that Tehran needs only five days to ramp up its uranium enrichment to 20 percent, a level at which the material could be used for a nuclear weapon.

The comments by Ali Akbar Salehi to Iranian state television on Tuesday followed repeated threats by US President Donald Trump to renegotiate or walk away from a historic 2015 nuclear deal.

"If there is a plan for a reaction and a challenge, we will definitely surprise them," said Salehi, who also serves as one of Rouhani's vice presidents.

"If we make the determination, we are able to resume 20 percent enrichment in at most five days."

He added: "Definitely, we are not interested in such a thing happening. We have not achieved the deal easily to let it go so easily. We are committed to the deal, and we are loyal to it."

Iran gave up the majority of its stockpile of 20 percent enriched uranium as part of the nuclear deal it struck with world powers, co-signed by Trump's predecessor, President Barack Obama.

The 2015 accord, which lifted sanctions on Iran, currently caps the country's uranium enrichment at five percent.

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