President Donald Trump claimed Thursday that Iran is not in compliance with a historic nuclear accord between the Islamic Republic and world powers.

The U.S. under Trump has twice certified that Iran is acting in line with the Joint Comprehensive Plan of Action (JCPOA), most recently on July 17, but has maintained Tehran is in violation of its spirit.

"I personally don't think they're in compliance," Trump told reporters in New Jersey. "I don't think they're living up to the spirit of the agreement."

"I think you'll see some very strong things taking place if they don't get themselves in compliance," he added.

Trump didn’t elaborate further on how Iran was not in compliance.

Trump threatened to pull the U.S. out of the accord during his 2016 run for the White House but has been met with the diplomatic blowback of doing so upon assuming office. None of the U.S.'s negotiating partners, including close European allies, want to do away with the JCPOA.

They were instrumental in providing Iran with relief from economic sanctions that allowed for the international community to have wide-ranging access to Tehran's nuclear program while placing restrictions on the program.

The International Atomic Energy Agency, which is tasked with monitoring the agreement's implementation, has repeatedly certified Iran's compliance with the 2015 accord.