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By Erin McClam

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.”

Related: Read the Full Agreement

Obama spoke after Iran and six world powers, led by the United States, reached the accord, under which Tehran agreed to curb its nuclear program in exchange for the easing of economic sanctions.

To opponents of the agreement in Congress, Obama said that "we don't make deals like this with our friends." He invoked American arms-control deals with the Soviet Union decades ago.

One of the opponents of the Iran deal, Republican Sen. Tom Cotton of Arkansas, told MSNBC immediately after Obama spoke that the deal was dangerous. He said he believed Congress would kill the agreement.

Secretary of State John Kerry, speaking from the site of the talks in Vienna, called it "the good deal that we sought."

"We were determined to get this right, and I believe our persistence paid off," he said.

One senior White House official cautioned that while the agreement was undoubtedly historic, it was not an "immediately transformative" moment.

"We're years away from judging its success," the official told NBC News.