British Prime Minister David Cameron said Sunday that the world “would face Iran with a nuclear weapon” if six powers, including the U.S., had not struck a historic nuclear deal with Tehran.

“I think it is so much better than the alternative. I think that if there wasn't a deal, I think we would face Iran with a nuclear weapon,” Cameron said on NBC’s “Meet the Press" on Sunday. “That would’ve given a terrible choice to the West of either enabling that — allowing that to happen — or a very difficult decision to take military action.”

The United Kingdom was part of the group known as the P5+1 — the five permanent members of the United Nations Security Council, plus Germany — that reached the landmark accord with Iran.

The group, which also includes France, Russia and China, agreed to a historic nuclear deal with Iran last week. Among the key details in the agreement: Iran can keep its nuclear program for research and peaceful purposes and it will get eventual relief from crippling economic sanctions. But if Tehran violates the agreement, sanctions will snap back.

Cameron said he spoke with Iranian President Hassan Rouhani about terrorism in the Middle East and the ongoing violence in Syria and Yemen. Cameron said to expect more battles with Iran on other issues.

“We shouldn't be naïve or starry eyed in any way about the regime that we're dealing with. I'm certainly not,” he told NBC's Chuck Todd in an exclusive interview with an American television network.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

“This is not a successful country,” Cameron later said. “It's not a successful economy. It struggles with infrastructure. It's got a pretty backward system in terms of justice and human rights. We should call it out on those things and be frank about those things and recognize that actually taking the nuclear issue off the table makes us safer.”

Cameron’s comments Sunday followed Secretary of State John Kerry’s continued insistence that the nuclear agreement with Iran is based on steps that are verifiable and based on evidence.

“Nothing in this agreement, nothing at all, is based on trust,” Kerry told Chuck Todd in a separate interview that also aired Sunday.

“The entire agreement is based on verification, accountability and steps we can take to respond to any violation by Iran.”

Kerry and the White House are already facing a very vocal opposition to the deal in the U.S. Sen. Tom Cotton, R-Ark., pushed back on the administration's defense of the deal, calling Iran a "terror-sponsoring, anti-American, outlaw regime."

"We should not be empowering such a regime to be a successful, regional power. We should be confronting them in every way. This deal though gives them $150 billion of sanctions relief," Cotton said.

Cotton also expressed doubt that Iran wouldn't cheat on the deal and said that "even if Iran obeys the deal, Iran is going to be a nuclear-weapon state in just ten years ... I don't think it's a good thing to give such an outlaw regime nuclear weapons capability."

He called on Congress to reject the deal.

Israel, too, has been critical of the deal. Israeli Prime Minister Benjamin Netanyahu has argued against the deal on multiple occasions, and criticized the talks in a March speech in front of a joint session of Congress.

“The preeminent terrorist state of our time should not have access to a vast nuclear capability that will ultimately give them nuclear weapons,” Netanyahu said during an April appearance on “Meet the Press” after a framework deal was announced, but before the final agreement was negotiated. “That's a concern for Israel, for the region, for the peace of the world.”

Cameron, in response to a question about criticisms from Israel and Gulf nations, argued that because the threat of a nuclear Iran is “off the table” now, the countries who negotiated the deal can now work with Iran on other issues.

“Let's put the pressure on Iran on the other behavior changes that we want to see, but recognize this was a deal worth doing,” he said. “You have to come back to the alternatives. If we had walked away from this negotiation and not made compromises, I think we would then see a nuclear-armed Iran.”