Washington (CNN) -- He doesn't trust Iran, vows it won't get nuclear weapons, and believes past rhetoric by its leaders threatening annihilation of Israel is unacceptable and kind of insane.
So why is Secretary of State John Kerry so adamant about getting time to try to negotiate an agreement that would further curb Iran's nuclear ambitions in exchange for lifting crippling economic sanctions?
The former Senator spent 2 1/2 hours at a House Foreign Affairs Committee
hearing on Tuesday defending the international negotiations last month that brought an interim deal with Iran intended to lead to a comprehensive agreement after six months.
Facing skeptical legislators from both parties, Kerry tried to assure them that he shares their mistrust of Iran while asking that they halt the drive for new sanctions for now to give negotiations, which also involve the other permanent members of the U.N. Security Council and Germany, a chance to succeed.
He bristled when yet another GOP legislator, Rep. Jeff Duncan of South Carolina, described the U.S. position as giving Iran the benefit of the doubt by not requiring the dismantling of all centrifuges needed to enrich uranium for nuclear weapons.
"I sat here and said we're skeptical. I sat here and said they've got to prove it," Kerry responded, adding "there's no benefit of any doubt here."
His takeaway message borrowed from former President Ronald Reagan's "trust but verify" guideline for a weapons deal with the Soviet Union, but Kerry modified it to reflect the lack of trust in Tehran's intentions.
"Test and verify," he said repeatedly in describing restrictions on Iran's program in the interim agreement, as well as the necessary monitoring and testing for a final agreement acceptable to President Barack Obama that would ensure Iran would be unable to develop nukes.
A bipartisan group of Senators is working on new sanctions legislation and the House may consider a similar measure, prompted by concern that the interim agreement eased some sanctions without achieving the goal of ridding Iran of its centrifuges and other technology needed to build a nuclear bomb.
However, the interim deal reached last month in Geneva prohibits new sanctions, and Kerry argued Tuesday that such a step was unnecessary at this point.
"They know that if they fail, sanctions will be increased," Kerry said of Iran. "We've said it a hundred times and you all have said it a hundred times and they know you're yearning to go do it but you don't need to do it. It is actually gratuitous in the context of this situation because you can do it in a week if you need to when we say, 'this ain't working, we need your help,' and believe me we'll be prepared to do that."
After Kerry's remarks Tuesday, the chairman of the Senate Banking Committee said the panel would hold off on considering new sanctions legislation for now.
The statement by Democratic Sen. Tim Johnson of South Dakota left open the possibility of Senate leaders taking up the bill without having it go through the committee.
Earlier, Kerry declared that "Iran will not acquire a nuclear weapon," calling the stance the centerpiece of President Barack Obama's foreign policy.
The interim agreement eases some $7 billion in economic sanctions in return for limiting aspects of Iran's nuclear program, Kerry told the committee.
Israel opposes that deal because it allows Iran -- a longtime enemy of the Jewish state -- to continue enriching uranium needed to develop nuclear weapons.
Prime Minister Benjamin Netanyahu has made clear that Israel would attack Iran's nuclear facilities if it felt threatened, and the negotiations are considered an effort to avoid a possible military confrontation in the volatile Middle East.
In Congress, legislators from both parties agree that tougher measures are needed.
"We are facing an immoral and very dangerous regime in Iran, one nearing a nuclear weapon," Rep. Ed Royce, the House Foreign Affairs Committee's Republican chairman, said at Tuesday's hearing.
"I am hard pressed to understand why we'd be letting up sanctions pressure at the very time its economy is on the ropes without getting an agreement which stops its centrifuges from spinning."
Others used more graphic language, with GOP Rep. Mo Brooks of Alabama comparing Iran's threats against Israel to Nazi Germany.
"What can you say to Israel and the rest of our allies in the Middle East to convince them that America is still a reliable ally, that America will enforce agreements with Iran or else, and that America is not ignoring history and repeating the 1930s Neville Chamberlain-like pattern of appeasement and retreat that helped trigger World War II and the death of tens of millions of people around the world?" Brooks asked.
Kerry responded by "condemning in the strongest language possible those expressions of hate and of, you know, sheer and utter insanity, almost, asking for a country to be wiped off the face of the map."
"That language is the most abhorrent kind of language you can find in any discourse of public life," he said. "It has no place in a reasonable world. It's unacceptable, and we should never hear that kind of language again."
Iranian officials have long said the country's nuclear intentions were peaceful. They also warned any new sanctions would scuttle the interim agreement, noting that language in the document specifies no new ones can occur.
Obama said over the weekend that he would accept a peaceful nuclear program in Iran, including modest uranium enrichment.
However, Royce said the key issue is whether an eventual final agreement negotiated on the world stage with Iran would permit it to "manufacture nuclear fuel."
"Unfortunately, the interim agreement raises some questions about this," he said. "My concern is that we may have bargained away our fundamental position, which is enshrined in six U.N. Security Council Resolutions -- and that fundamental agreement is that Iran should not be enriching and reprocessing. We may bargain that away for a false confidence that we can effectively check Iran's" misuse of the nuclear weapons technologies.
GOP Rep. Matt Salmon of Arizona said the Iranians "can get all the nuclear material they need for power by purchasing it from other countries," adding that "they don't need to enrich it themselves."
Kerry stopped short of declaring a final agreement with Iran would prevent any uranium enrichment capability for Tehran, saying such details must be worked out. He noted that the interim agreement reached last month requires full consensus on such matters.
To legislators calling for more sanctions, Kerry said economic strictures alone had failed to prevent Iran from expanding its centrifuges in recent years as it made progress toward developing a nuclear weapon.
"The issue here is what are we going to do about it so we don't have a sudden breakout," he said, adding that the interim agreement is a step toward that.
"In order to weaponize, you have to have highly enriched uranium. Under the agreement, they can't have highly enriched uranium."
Royce, though, noted that Iran has "a history of deceiving the international community about its nuclear program, and is pursuing a ballistic missile program in violation of U.N. Security Council Resolutions," adding that it "simply can't be trusted with enrichment technology, because verification efforts can never be foolproof."
CNN Chief Congressional Correspondent Dana Bash contributed to this report.