US President Donald Trump on Thursday insisted Iran has not acted in keeping with a deal to curb its nuclear program, days before he must decide on the future of the accord.

"They have not lived up to the spirit of the agreement," said Trump, who appeared poised to withhold certification of Iran's compliance, leaving Congress to weigh sanctions that could scupper the deal.

"The Iranian regime supports terrorism and exports violence and chaos across the Middle East," Trump said as he met military leaders to discuss the issue.

"That is why we must put an end to Iran's continued aggression and nuclear ambitions" he said. "You will be hearing about Iran very shortly."

Ahead of the October 15 deadline, several officials familiar with White House deliberations told AFP Trump has made it clear he does not want to certify Iran's compliance with the accord, flying in the face of advice from some of his closest advisors.