Sixty national security leaders, ambassadors, military leaders and former Cabinet secretaries signed a letter released on Monday in support of the nuclear deal with Iran.

The bipartisan group of signatories includes former Secretary of State Madeleine Albright; former national security advisers Zbigniew Brzezinski and Brent Scowcroft; former Sens. Nancy Landon Kassebaum, Tom Daschle, Carl Levin and George Mitchell; former defense official Michele Flournoy and Thomas Pickering, the former ambassador to Israel, Russia, India and the United Nations.

"No agreement between multiple parties can be a perfect agreement without risks," the letter said. "We believe without this agreement, the risks to the security of the U.S. and its friends would be far greater. We have also not heard any viable alternatives from those who oppose the implementation" of the deal.

The U.S. and five other world powers reached an agreement last week with Iran to curb its nuclear program in exchange for sanctions relief.

The Security Council unanimously endorsed the landmark nuclear deal Monday and authorized a series of measures leading to the end of U.N. sanctions that have hurt Iran's economy.

The White House has been heavily lobbying Congress, which has 60 days to review the agreement, to vote to approve or disapprove of the deal, or take no action.