By Patricia Zengerle
WASHINGTON (Reuters) - A dispute among Republican senators over changes to an Iran nuclear review bill on Thursday threatened the measure's chances of being passed by the U.S. Congress, leaving Senate leaders scrambling for a way to advance the legislation.
Two Republican senators, Tom Cotton and Marco Rubio, used an unorthodox procedural move to try to force the Senate to vote on their amendments to a bill authored by another Republican senator, Bob Corker, that would give Congress the right to review an international nuclear agreement with Iran.
Rubio, a 2016 presidential hopeful, and Cotton, a leading congressional critic of President Barack Obama's Iran policy, want to toughen the bill with amendments including adding a requirement that Iran recognize Israel's right to exist as part of any nuclear deal.
Senate aides said the two made their move on Thursday just as Republicans and Democrats were finalizing an agreement on how to handle at least 66 amendments proposed by Republicans to the Iran Nuclear Review Act.
"I have a sense that the context of this has just changed," Corker said. "I regret that."
The Senate has been engaged in intense debate over the legislation, a compromise version of the bill reached in the Senate Foreign Relations Committee last week in an effort to avoid a presidential veto.
The White House had said some of the stronger provisions of the original measure would have threatened delicate international talks between Iran and world powers over Tehran's nuclear program. The negotiators have given themselves until the end of June to reach a final agreement, which members of Congress want to review.
Corker and Ben Cardin, the committee's Republican chairman and top Democrat, have been arguing against so-called poison pill amendments. They say such amendments would alienate many Democrats who now support the measure and prompt a veto.
Senators voted down two such controversial amendments earlier this week.
There was some optimism about the bill's long-term prospects, however. Senate aides said they expected the Republican Majority Leader, Mitch McConnell, would take steps as early as Monday to stop debate on the bill and allow a vote on a "clean" version, without amendments.
But a spokesman said late on Thursday that McConnell had not yet said whether he would do so, and that Senate leaders were still trying to find a way to have votes on amendments.
(Reporting by Patricia Zengerle; Editing by Cynthia Osterman)