WASHINGTON (JTA) — Top lawmakers of both parties pressed U.S. Secretary of State John Kerry on his plea to Congress not to pass new Iran sanctions while nuclear talks are underway.

Kerry on Tuesday testified before the U.S. House of Representatives Foreign Affairs Committee in his first public congressional appearance since last month’s interim sanctions-for-nuclear rollback brokered between the major powers and Iran.

He repeated his pleas not to add new sanctions, saying that this would drive away allies who have helped sustain the existing sanctions that brought Iran to the table.

“We’re asking you to give our negotiators and our experts the time and the space to do their jobs, and that includes asking you while we negotiate that you hold off imposing new sanctions,” Kerry said. “We have an obligation to give these negotiations an opportunity to succeed. And we can’t ask the rest of the P5+1 and our partners around the world to hold up their ends of the bargain if the United States isn’t going to uphold its end of the bargain.”

The P5+1 refers to Russia, China, Britain, France, the United States and Germany, the major powers that brokered the deal with Iran.

Questions from the committee, led by Rep. Ed Royce (R-Calif.), focused on proposals in Congress to further enhance sanctions as a means of extracting further concessions from Iran.

Royce noted with dismay that the interim deal preserved Iran’s capacity for low-level uranium enrichment.

He echoed Israeli Prime Minister Benjamin Netanyahu in saying that Iran must not preserve any enrichment capacity as part of a final deal. “It simply can’t be trusted with enrichment technology, because verification efforts can never be fool proof,” Royce said.

“An agreement in which Iran purchases and returns spent nuclear fuel for energy generation is one thing, but allowing enrichment is too high risk, going beyond the lines of realistic international control,” Royce said.

President Obama and others have indicated that a final deal likely would include a limited enrichment capability.

Rep. Eliot Engel (D-N.Y.), the ranking Democrat on the committee, pressed Kerry on why Congress should not pass sanctions that would go into effect only if Iran reneged on the deal.

“Why does the Administration strongly oppose congressional action on Iran sanctions legislation that makes clear new sanctions will not be imposed unless Iran violated the terms of the interim deal?” Engel asked.

Kerry did not fully respond except to say that such sanctions, even if structured only to kick in should Iran violate terms, would be “gratuitous” and alienate allies.