Vice President Joe Biden, right, chats with Secretary of State John Kerry, left, after a closed door meeting Wednesday with members of the Senate Banking Committee that included a discussion on a new sanctions bill on Iran. (JIM LO SCALZO/EPA)

The Obama administration struggled Wednesday to head off new congressional sanctions that it fears could kill a proposed nuclear deal with Iran before it can be finalized.

During a visit to Capitol Hill, Secretary of State John F. Kerry and Vice President Biden faced strong skepticism, including from leading Democrats, who suggested the White House is being snookered by the Iranian leadership.

Kerry warned that although tough economic sanctions have worked as intended to push Iran to the bargaining table, piling on now could drive the country away.

“The risk is that if Congress were to unilaterally move to raise sanctions, it could break faith in those negotiations, and actually stop them and break them apart,” Kerry said before a closed session of the Senate Banking Committee. “What we’re asking everyone to do is calm down, look hard at what can be achieved and what the realities are.”

Afterward, Senate Republicans scoffed at the administration presentation.

“I do think we ought to accelerate sanctions,” Sen. Mark Kirk (Ill.) told reporters. “The pitch was very unconvincing” and insufficient for Israeli security, he said. Israel has fiercely objected to a proposed deal with Iran.

Sen. Bob Corker (R-Tenn.) said he was disappointed in what he called a thin presentation, despite the classified setting.

The Democratic-led committee is considering new sanctions but had agreed to hold off while Kerry and other foreign ministers bargained with Iran last week. The latest sanctions package was overwhelmingly approved by the Republican-led House in July.

“We must make it crystal clear to Tehran that even tougher sanctions are coming down the pike if the regime is unwilling to take concrete and verifiable steps to freeze and then dismantle its nuclear weapons program,” said Rep. Eliot L. Engel (N.Y.), ranking Democrat on the House Foreign Affairs Committee.

Engel accused the administration of leaving Congress in the dark about the talks with Iran.

“I hope the administration understands that we cannot take their concerns fully into account — nor truly understand events at the negotiation table, or grasp the impact our legislation may have on their efforts — if they do not do a better job of keeping Congress informed,” he said.

Nuclear talks with Iran had made no progress for months before the June election of President Hassan Rouhani, who has a mandate to seek a deal that can reduce economic sanctions that have severely damaged Iran’s oil-based economy.

A deal seemed close last week, but when talks broke off with much finger-pointing, congressional efforts to add further economic penalties resumed.

The potential deal has also opened a rift with Saudi Arabia and caused rancor even among the nations negotiating alongside the United States. France balked last week at language largely written by the United States, forcing a rewording of the proposed text, diplomats familiar with the negotiations said. They spoke on the condition of anonymity because the talks are continuing, and terms of the offer are not public.

The White House said that President Obama spoke Wednesday with French President François Hollande and that they reaffirmed “full agreement” on the proposal.

Biden and Kerry also lobbied Senate Democratic leaders, as surrogates argued elsewhere that the potential deal offers a path to defuse fears that Iran will build a nuclear weapon. Administration officials steered clear of a public argument with Israel, whose rejection of the proposal has found support in Congress.

“We think that Israel and the United States and all of our allies and partners have the same goal, which is to prevent Iran from getting a nuclear weapon,” White House national security adviser Susan E. Rice said at an Atlantic magazine forum. “If we can achieve that through a peaceful negotiated settlement, that’s what the American people want, and I think that’s what the people of the region and around the world should want.”

Negotiators will meet again Nov. 21 in Switzerland. Kerry does not plan to attend but could reconsider if a deal appears imminent, spokeswoman Jennifer Psaki said.

Kerry and Biden, accompanied by the lead State Department negotiator and the Treasury Department’s sanctions chief, were arguing for a grace period of a few more weeks to see whether a deal can be struck.

“If this doesn’t work, we reserve the right to dial back up the sanctions,” Kerry told reporters. “I will be up here on the Hill asking for increased sanctions, and we always reserve the military option. So we lose absolutely nothing, except for the possibility of getting in the way of diplomacy and letting it work.”

Visiting Washington mainly to lobby against the deal, conservative Israeli economics minister Naftali Bennett said the United States and other world powers are sliding toward an accord that weakens sanctions permanently.

“We’re afraid that the temporary deal will become the final deal,” Bennett said in an interview with The Washington Post.

Joby Warrick contributed to this report.