WASHINGTON — Congressional figures took a hesitant approach to a newly brokered nuclear deal with Iran early Sunday, as the White House scrambled to gain backing from lawmakers on the agreement.

A senior administration official said late Saturday night that the White House was speaking directly with Congress about the deal, which critics complain allows Iran to retain too much capacity to prepare nuclear weapons.

As details of the deal emerged, Republican congressional leaders assessed the possibility of continuing with harsher sanctions legislation and summoning Secretary of State John Kerry to explain how the deal was struck.

House Majority Leader Eric Cantor (R-VA) said that he “remains concerned that this deal does not adequately halt Iran’s enrichment capabilities.” In a statement released shortly after a deal was announced, Cantor warned that “the United States must remain vigilant and respond immediately and severely to any cheating or wrongdoing by Iran.” Anticipating the furious responses voiced by US allies Israel and Saudi Arabia, Cantor added that the US “must rebuild our alliances in the region and stand firmly with our closest partners against Iranian aggression.”

Cantor’s concerns were echoed by House Foreign Affairs Committee Chairman Ed Royce (Republican of California), who said that he has “serious concerns that this agreement does not meet the standards necessary to protect the United States and our allies.”

Royce implied that he would summon Kerry before his committee to “address the many concerns with this agreement,” which he said entailed a dismantling of the “sanctions pressure built up over years.”

Even some members of the Democratic minority in the House offered limited optimism regarding the deal. Rep. Eliot Engel, the leading Democrat on Royce’s committee, said that he was “concerned that this interim agreement does not require Iran to completely halt its enrichment efforts or dismantle its centrifuges.”

Engel offered a slightly more optimistic perspective, however, adding that he “hopes that over the next six months, Iran takes the necessary steps to finally end its quest for a nuclear weapons capability.”

Some of Engel’s Democratic colleagues were more positive. Rep. Adam Smith (Democrat of Washington), the ranking member on the House Armed Services Committee, described the deal as “a positive step in the right direction.”

“I applaud the administration for making progress on this important national security issue,” Smith added. “This preliminary step should serve as a bridge to a long-term deal. This interim agreement gives us the chance to make significant progress towards the goal we and our allies seek: preventing Iran from obtaining a nuclear weapon. While today’s announcement represents serious progress, far more work remains to be done.”

Dovish Israel lobby J Street threw its weight behind the agreement, which it called a “significant first step.”

“Secretary of State John Kerry, Under Secretary of State Wendy Sherman and their negotiating partners deserve our thanks for their clear-eyed pursuit of a diplomatic resolution, which remains the most desirable way to achieve the shared goal of the US, Israel and all parties with a stake in the security and stability of the Middle East,” the group said in a statement.

Republican senators, still recoiling from a bitter political loss on filibuster reform last week, did not mince words. Sen. Lindsey Graham (Republican of South Carolina) tweeted that “unless the agreement requires dismantling of the Iranian centrifuges” – which it does not – “we really haven’t gained anything.” Sen. John Cornyn (Republican of Texas) was far more cynical in his 140 characters, tweeting that it is “amazing what WH will do to distract attention from O-care” [Obamacare].

Sen. Mark Kirk (Republican of Illinois) released a statement promising that despite the agreement, he “will continue working with my colleagues to craft bipartisan legislation that will impose tough new economic sanctions if Iran undermines this interim accord or if the dismantlement of Iran’s nuclear infrastructure is not underway by the end of this six-month period.” Sen. Marco Rubio (Republican of Florida), agreed, warning that the deal “makes a nuclear Iran more likely” and calling on Congress to increase sanctions “until Iran completely abandons its enrichment and reprocessing capabilities.”

“This agreement is a blow to our allies in the region who are already concerned about America’s commitment to their security and it sends the wrong message to the Iranian people,” he continued in lengthy written statement. “Just days ago, Iran’s Supreme Leader Khamenei, who will oversee implementation of this agreement, was calling Israel a ‘rabid dog’ and accusing the United States of war crimes. Yet today President Obama is asking us to accept the pledges of this regime, which still refuses to end its support for terrorism and admit the illicit nature of its past nuclear work.”