US President Barack Obama declared Tuesday that the landmark nuclear deal with Iran is built on verification, not trust alone, and he threatened to veto any attempt by Congress to stop it.

US President Barack Obama declared Tuesday that the landmark nuclear deal with Iran is built on verification, not trust alone, and he threatened to veto any attempt by Congress to stop it.

"This deal demonstrates that American diplomacy can bring about real and meaningful change, change that makes our country and the world safer and more secure," he said in an early-morning statement from the White House.

He said that the United States had "negotiated from a position of strength and principle" and "stopped the spread of nuclear weapons in this region." Walking away from the deal, he said, could touch off a nuclear arms race in the most volatile region in the world.

"Put simply," the president said, "no deal means the chance of more war in the Middle East."

Foreign ministers from Iran and major powers have signed on Tuesday the final agreement regarding the nuclear program of the Islamic Republic in a win-win deal for both sides.