Congressional critics have expressed skepticism about Iran's trustworthiness.
Secretary of State John Kerry said Sunday that the prospect of a final nuclear deal with Iran is "not a question of trust," but of verification that the Iranians are giving up the prospect of nuclear weapons.
Appearing on CNN's State of the Union, Kerry said, "Verification is the key," adding that the United States enters into more negotiations with Iran "with eyes absolutely wide open. We have no illusions."
Said Kerry: "We're trying to set up a process by which we can verify, know what we're doing, restraining the program while we negotiate the comprehensive deal."
Six world powers reached an interim agreement late Saturday night with Iran on its disputed nuclear program after four days of talks in Geneva.
In the six-month interim deal, Iran agreed to limit nuclear activities in return for relief of up to $7 billion in sanctions that have hurt its economy.
Kerry promoted the interim Iran agreement on Sunday talk shows, reaching out to critics in Israel and stressing that Tehran must prove its willingness to forgo nuclear weapons.
"Israel and the United States absolutely share the same goal here," Kerry said on ABC's This Week. "There is no daylight between us with respect to what we want to achieve, at this point. We both want to make it certain Iran cannot have a nuclear weapon. And Iran cannot be in a place where they can break out and suddenly get that nuclear weapon."
Kerry spoke as Israeli Prime Minister Benjamin Netanyahu denounced the agreement reached by the U.S. and allied negotiators.
"What was reached last night in Geneva is not a historic agreement, it is a historic mistake," Netanyahu said. "Today the world became a much more dangerous place because the most dangerous regime in the world made a significant step in obtaining the most dangerous weapons in the world."
President Obama is expected to speak with Netanyahu by phone soon, probably on Sunday.
Both Kerry and President Obama have called on Congress to forgo additional sanctions on Iran, saying they could kill the interim agreement -- but some lawmakers have indicated they will push forward anyway, expressing skepticism about Iran's trustworthiness.
One prominent Democrat -- Sen. Charles Schumer of New York -- said the deal "does not seem proportional" because "Iran simply freezes its nuclear capabilities while we reduce the sanctions."
The "disproportionality" of the deal "makes it more likely that Democrats and Republicans will join together and pass additional sanctions when we return in December," Schumer said.
Republicans like Sen. Lindsey Graham of South Carolina have also criticized the agreement.
Sen. Charles Murphy, D-Conn., said the agreement should be given a chance to work, saying that "the initial six-month framework gives us a chance to test Iranian intentions before reaching a more comprehensive agreement to prevent a nuclear Iran."
Sen. Bill Nelson, D-Fla., issued a brief statement: "It is a choice between a pause or imminent war. I choose a verifiable pause."
Over in the House, Rep. Eliot Engel, D-N.Y., top Democrat on the House Foreign Relations Committee, said the interim agreement should have forced Iran to give up nuclear enrichment now. He called the agreement "disappointing" during an appearance on CNN.
"I do think sanctions should always be hanging there, because that's what brought Iran to the table in the first place," Engel said. "And I don't think you make them bargain a good faith by going squishy."
Rep. Ed Royce, R-Calif., the committee chairman, denounced the agreement, telling CNN's State of the Union that Iran is "a state sponsor of terrorism trying to get a bomb."
Iran says its enrichment program is designed to generate energy for peaceful domestic purposes.