Washington DC - President Donald Trump's national security adviser on Sunday called for the "full dismantlement" of Iran's nuclear program.

"All options are on the table, and it is time for Iran to walk away completely from its desire to have a nuclear weapon," National Security Advisor Mike Waltz told US broadcaster CBS.

Waltz warned that if Iran had nuclear weapons, "the entire Middle East would explode in an arms race."

"That is completely unacceptable to our national security," Waltz added.

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Earlier this month, Trump wrote a letter to Iranian Supreme Leader Ayatollah Ali Khamenei with a view to possible nuclear negotiations.

"I've written them a letter saying, 'I hope you're going to negotiate because if we have to go in militarily, it's going to be a terrible thing,'" Trump said in an interview.

Khamenei has so far rejected negotiations with Washington, but the Iranian government has sent mixed signals.

In his first term in office, Trump unilaterally withdrew from the 2018 Vienna nuclear pact, which was intended to restrict Iran's nuclear program in return for the lifting of sanctions. After that, Tehran also no longer adhered to the terms of the agreement.