US Republican lawmakers on Wednesday called for greater say in any deal reached between the West and Iran over the Islamic republic's controversial nuclear program.

With negotiations to end Iran's years-long nuclear standoff with the United States and other Western powers recently extended for an additional four months, until November, five senators introduced legislation that would compel President Barack Obama to bring any final deal before Congress for its approval.

Many lawmakers have been dubious about the talks that began in late January and were supposed to have reached a deal by July 20.

The West believes Tehran is seeking to build an atomic bomb, but Iran insists its efforts are purely for civilian use.

"Any final agreement of a matter of this consequence should be reviewed by this body, should come before Congress, and should have the ability of Congress to provide oversight over it," Senator Marco Rubio told the chamber.

Failure to let US lawmakers vote on any final nuclear agreement would leave the United States vulnerable to "a terrible deal" that could put Americans in danger, Rubio said.

The legislation would prevent a further extension of negotiations, reimpose any eased sanctions if Iran showed it was cheating on its commitments under any future agreement, and block the deal's implementation if a veto-proof majority of Congress disapproves of it.

Fellow sponsor Senator Bob Corker, the top Republican on the Senate Foreign Relations Committee and a key architect of US sanctions on Iran that helped bring Tehran to the table, said he backed the negotiations and hopes they will ultimately bear fruit.

"But if and when they reach an agreement, let's bring all the details out in the open," Corker said.

"Let's examine the agreement in its entirety and let's determine that it's in our national security interest."

Senator Lindsey Graham said stopping Iran's pursuit of a nuclear weapon "is the most important foreign policy decision in generations."

"Congress played a fundamental role in enacting sanctions against Iran and should have a say whether this agreement is strong enough to lift sanctions."

A large majority of members of the House of Representatives voiced similar demands earlier this month, signing a letter to Obama saying that "any permanent sanctions relief demands congressional approval."