Pentagon chief James Mattis backs Iran nuclear deal ahead of deadline

US Defence Secretary James Mattis said on Tuesday that Iran was fundamentally in compliance with its nuclear deal, as President Donald Trump's administration weighs whether the 2015 agreement serves US security interests.

Trump faces a 15 October deadline for certifying that Iran is complying with the pact, a decision that could sink an agreement strongly supported by the other powers that negotiated it, including Britain, China, France, Germany, Russia and the European Union.

"I believe that they fundamentally are. There have been certainly some areas where they were not temporarily in that regard, but overall our intelligence community believes that they have been compliant and the IAEA also says so," Mattis said during a House of Representatives hearing, using an acronym for the International Atomic Energy Agency.

Asked by Senator Angus King if he thinks there is “national security interest” to keep the agreement, Mattis said: “Yes, sir. I do.”

Joint Chiefs of Staff Gen. Joseph Dunford also voiced support for the accord, which saw Iran significantly curb its nuclear programme in exchange for lifting economic sanctions imposed by Washington.

"Iran is not in material breach of the agreement," Dunford told lawmakers. "And I do believe the agreement, to date, has delayed the development of nuclear capability by Iran."

Trump has sent mixed signals about the pact. As a presidential candidate, he vowed to “rip up” the deal, which was signed under his predecessor, Barack Obama. He later promised to re-negotiate it. But the US president recertified the deal in July.

At the UN General Assembly last month, Trump hinted that he could pull the US out of the agreement.

"The Iran deal was one of the worst and most one-sided transactions the United States has ever entered into," he said on 19 September. "Frankly, that deal is an embarrassment to the United States, and I don’t think you’ve heard the last of it - believe me."