Mattis's expression of support for the 2015 agreement curbing Iran's nuclear program was in sharp contrast with Trump's blunt assessment that the deal is an "embarrassment."
Asked during a Senate hearing whether he believed it was in the national interest, Mattis replied: "Yes, senator, I do."
"If we can confirm that Iran is living by the agreement, if we can determine that this is in our best interest, then surely we should stay with it."
"I believe at this point in time, absent indication to the contrary, it is something that the president should consider staying with," he said.
He has so far certified that Iran is in compliance with the agreement but has indicated the next deadline on October 15 will be crucial.
Iran and the other signatories -- China, Russia, France, Britain and Germany -- defend the deal as a guarantee of the peaceful, non-military purposes of Tehran's nuclear program.
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