By Patricia Zengerle
WASHINGTON (Reuters) - The U.S. Senate Banking Committee voted 18-4 on Thursday to advance a bill that would toughen sanctions on Iran if international negotiators fail to reach an agreement on Tehran's nuclear program by the end of June.
However, the bill is not expected to come up for a vote in the full Senate until at least March 24. Ten Democrats, including the measure's co-author, Senator Robert Menendez, announced an agreement earlier this week to hold off for two months to allow time to reach a diplomatic solution.
Republicans would need those votes to pass the bill, and even more votes to override a veto threatened by Democratic President Barack Obama, who has called the measure a threat to the continuing nuclear talks with Iran.
In the committee, only four Democrats voted against the bill, which was also sponsored by Republican Senator Mark Kirk. The other six joined the panel's 12-member Republican majority to pass it.
"This legislation has been carefully calibrated to achieve our ultimate goal, which is to prevent Iran from achieving nuclear weapon capability," Menendez said.
The panel's top Democrat, Sherrod Brown, was one of the no votes. He called on lawmakers to wait until June to pass any more sanctions, reflecting an intense debate in Congress about how it should best seek to influence the talks on Iran's nuclear program.
"If negotiations fail, Congress and the president will join hands in applying greater pressure. And we will be in a far better position to ask the rest of the world to join us," Brown said.
Separately, a White House spokesman issued another veto threat on Thursday, saying Obama would veto a bill being developed by Republican Senators Bob Corker and Lindsey Graham that would require congressional approval for any nuclear deal with Tehran.
After more than 18 months of negotiations, the United States, Britain, China, France, Germany and Russia have agreed with Iran to try to reach a political understanding by the end of March, with a view to a full-blown deal by a self-imposed June 30 deadline.