(Reuters) - Opponents of Iran's initial agreement to curb its nuclear program are being "disingenuous" when they say the deal could still allow the Middle Eastern state to build nuclear weapons, the head of the Central Intelligence Agency said on Tuesday.

The initial accord reached last week between Iran and major world powers - which would lift crippling economic sanctions in exchange for Iran's agreement to step back from developing nuclear weapons - is likely the most realistic deal that could be reached, CIA Director John Brennan told an audience of students and faculty at Harvard University in Cambridge, Massachusetts, just outside Boston.

"The individuals who say that this deal provides a pathway for Iran to a bomb are being wholly disingenuous, in my view, if they know the facts and understand what is required for a program," Brennan said at Harvard's John F. Kennedy School of Government. "I certainly am pleasantly surprised that the Iranians have agreed to so much here."

Democrats in Washington are joining forces with Republican leaders who were early critics of the deal in supporting a bill that would give Congress the ability to approve or reject sanctions relief, a move that U.S. President Barack Obama said could undermine the negotiations at a critical stage.

Brennan, who has headed the U.S. spy agency since 2013, said he understood that some critics of the deal were wary that even with an accord Iran would have the ability "to cause more trouble" in the Middle East, where neighboring countries including Iraq are fighting violent groups including the Islamic State.

"That's a legitimate issue, concern and argument but that�s why I say what they shouldn't be doing is trying to pull apart this deal ... that's as solid as you're going to get," Brennan said. "You're not going to get the Iranians to just totally dismantle everything and say, 'OK, we're not going to pursue any type of nuclear capability from a peaceful perspective."

The deal has also been criticized by Israel, where Prime Minister Benjamin Netanyahu called Iran's nuclear ambitions an existential threat to his country.

Brennan said it was a hopeful sign that the Iranian regime was willing to engage in eight days of talks in Switzerland, noting that President Hassan Rouhani had "much greater reasonableness."

By Reuters