House Speaker John Boehner: We will do everything we can to destroy historic nuclear deal with Iran
US House Speaker John Boehner, seen here on July 8, said the landmark deal gives too much leeway to Iran (AFP Photo/Mandel Ngan)

Top US Republicans expressed skepticism about a historic nuclear deal reached Tuesday with Iran, saying it gives Tehran too much room to maneuver and does not safeguard American security interests.

Some in Congress have already said they are prepared to reject the deal because it does not comprehensively halt Tehran's enrichment process or permanently close the door on its development of a nuclear weapon.

House Speaker John Boehner blasted the deal as "unacceptable," saying that if it is "as bad a deal as I think it is at this moment, we'll do everything we can to stop it."

He warned it would only "embolden" Iran and even could trigger a global nuclear arms race.

Now that President Barack Obama announced his support for the agreement between six world powers and Iran, finalized in Vienna after marathon talks, the attention in Washington now shifts to the Republican-controlled Congress.

Under legislation passed in May, they will have 60 days -- much of it during the lawmakers' traditional August recess -- to conduct their review. Debate will take place during several hearings on the nuclear deal.

Congress could then vote to approve the accord or reject it, or do nothing.

Obama has said he would veto a resolution of disapproval. Overriding that veto would require a two-thirds majority in both the Senate and House of Representatives -- a heavy lift in Congress.

Obama is barred from lifting any Iran sanctions during the review period. And should Congress later determine that Iran failed to abide by the agreement, it could reinstate sanctions waived by the president.

- 'Deep skepticism' -

It did not take long for Republicans to make their concerns known.

"I begin from a place of deep skepticism that the deal actually meets the goal of preventing Iran from obtaining a nuclear weapon," Senate Foreign Relations Committee chairman Bob Corker said in a statement.

Congress, he said, "will need to scrutinize this deal and answer whether implementing the agreement is worth dismantling our painstakingly-constructed sanctions regime that took more than a decade to establish."

Members from both parties stressed it will be a tough sell in Congress.

"I'm concerned the red lines we drew have turned into green lights, that Iran will be required only to limit rather than eliminate its nuclear program, while the international community will be required to lift the sanctions," warned Senate Democrat Robert Menendez, an architect of stiff sanctions against Iran.

"The bottom line is: The deal doesn't end Iran's nuclear program –- it preserves it."

Republican Senator Tom Cotton, who penned an explosive letter in March to Iran's leaders, described the deal as "a terrible dangerous mistake" that will pave the way for a nuclear Iran.

"The American people are going to repudiate this deal, and I believe Congress will kill the deal," he told MSNBC.

The top Democrat on the Senate Foreign Relations Committee, Ben Cardin, said Congress must "vigorously and judiciously review" the accord.

"There is no trust when it comes to Iran," Cardin said.

Several lawmakers warned that the accord rewards Iran with billions of dollars in sanctions relief.

Senator Lindsey Graham, a 2016 presidential candidate, said Obama and Secretary of State John Kerry have been "dangerously naive" in their dealings with Tehran.

"You have taken the largest state sponsor of terror on the planet and given them money to increase their terrorist activities" by funding groups like Hezbollah and Hamas, as well as Syrian President Bashar al-Assad, Graham said.