"We will continue to work alongside our allies and partners to ensure that Iran can never acquire a nuclear weapon, and will work with others to address the range of Iran's malign influence," Mattis told a Senate panel.

"This administration remains committed to putting the safety, interests and well-being of our citizens first."

Mattis, a retired four-star general who saw his Marines killed by Tehran-backed militias in Iraq, has frequently lambasted Iranian actions in the Middle East.

But he has been a staunch advocate of working with allies and became a quiet defender of the Iran deal as Trump mulled pulling out.

In October, he said it was in the US national interest to remain in the deal.

In January, he said the Iran deal was "imperfect" but added that "when America gives her word, we have to live up to it and work with our allies."

Last month, he said the deal allowed for "pretty robust" inspections of Iranian facilities.

Mattis risks being isolated by Trump's more hardline coterie of advisors, including national security advisor John Bolton, an Iraq War-era hawk who has advocated military action in both Iran and North Korea.