Defense Secretary Jim Mattis said Tuesday the United States should remain in the nuclear deal negotiated during the Obama administration that constrains Iran's ability to build a nuclear arsenal.

Sen. Angus King of Maine asked Mattis during a congressional hearing if he thinks it's in the national security interests of the United States to stay a part of the international accord.

Mattis said, "Yes, senator, I do."

President Donald Trump has called the deal the worst agreement ever negotiated by the United States.

Trump has repeatedly said that he's inclined not to certify Iranian compliance after having twice found the country compliant at earlier deadlines. Denying certification could lead the U.S. to reintroduce sanctions, which in turn could lead Iran to walk away from the deal or restart previously curtailed nuclear activities.

Officials have said Trump might use the Oct. 15 deadline for certifying to Congress whether Iran is in compliance with the nuclear deal to either declare Iran in violation or determine that the agreement is no longer in the national security interest of the U.S.

Congressional Democrats are increasingly worried Trump's distaste for the Iran nuclear deal will lead him to abandon the accord and imperil the ability to contain Iran's nuclear program.

Mattis' statement gave them a strong argument in the discussion.

"If we can confirm that Iran is living by the agreement, if we can determine that this is in our best interest, then clearly, we should stay with it," Mattis said. "I believe, at this point in time, absent indications to the contrary, it is something the president should consider staying with."

Sen. Tom Cotton, R-Ark., who dined with Trump Monday night along with several other lawmakers, said Tuesday that he discussed Iran with the president.

"He didn't tell me, he said he's made a decision but he's not telling anyone. I strongly urged him to not certify the deal," Cotton said.

Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said last month that Iran is adhering to its obligations under the nuclear agreement, known officially as the Joint Comprehensive Plan of Action. He stressed that his concern is about Iran's behavior in other areas, such as its development of ballistic missiles and its support for extremist groups.

Dunford declined to say publicly what advice he has given Trump on whether to recertify Iran's compliance with the nuclear deal.

Iran has ruled out any renegotiation of the agreement and has said that any abandonment of the deal would lead it to immediately resume enrichment of uranium. Iran also has said it has no intention ever of acquiring nuclear weapons, but the U.S. and Israel are among the countries that do not accept those assurances, citing Iran's past nuclear activities.


Associated Press writer Erica Werner contributed to this report.