Fifty-nine senators now back a new sanctions package they say would increase the pressure on Iran to make nuclear concessions, according to congressional aides.
The count brings Congress closer to passing a bill the Obama administration considers a threat to a historic diplomatic opportunity.
The senators in favor include every Republican except Jeff Flake of Arizona and Rand Paul of Kentucky, aides said. Sixteen Democrats are on board including Sen. Chuck Schumer of New York, a top ally of President Barack Obama. Many more are understood to be sitting on the fence.
With the House of Representatives strongly backing more economic pressure on Tehran, the Senate is now close to the 60 votes needed to pass most legislation. And advocates are not far away from rounding up the 67 votes they would need to override a presidential veto, which the White House has vowed if the bill makes it out of Congress. Aides provided the latest tally on condition of anonymity because they weren't authorized to speak publicly on the matter.
Administration officials fear the new economic restrictions could jeopardize a breakthrough interim nuclear deal that world powers reached with Iran in Geneva in November, as well as ongoing negotiations on a final agreement that would end the threat of Iran developing nuclear weapons. By scuttling the diplomatic chances, the administration argues, Congress would be making a potential war with Iran more likely.
"The need for additional prospective sanctions is already clear," Sen. Bob Menendez, D-N.J., who drafted the bill, said Friday. Since the interim accord, he argued, Iran has made several announcements related to its uranium and plutonium programs that reinforce the need for Washington not to let up on the pressure. "This is hardly a march to war," Menendez said.
The legislation would blacklist several Iranian industrial sectors and threaten banks and companies around the world with being banned from the U.S. market if they help Iran export any more oil. The provisions would only take effect if Tehran violates the six-month interim deal or lets it expire without a comprehensive nuclear agreement.
Twenty-six senators co-sponsored the bill when it was introduced last month. Despite the growing tide of support among Democrats and Republicans, several key lawmakers still are opposed.
Ten Democratic committee chairmen, including influential senators such as Dianne Feinstein of California and Carl Levin of Michigan, have urged a pause in sanctions while the Obama administration and its diplomatic partners test whether Iran's moderate-leaning President Hassan Rouhani will adhere to the Geneva agreement. Senate Majority Leader Harry Reid held off a vote during defense bill negotiations before Christmas.
The House approved similar legislation last July by a 400-20 vote and would likely pass the new sanctions by an overwhelming margin.
Sanctions advocates say the administration needs the added leverage of sanctions just around the corner to secure a better deal than the last one. In Geneva, world powers promised Tehran some $7 billion in sanctions relief for actions that only freeze, not dismantle, central elements of the nuclear program. Iran insists its program is solely for peaceful energy and medical research purposes.
But the Obama administration cites several concerns over the timing of the bill and the realism of enforcing provisions such as a global ban on Iranian oil exports by 2015.
The legislation "would be counterproductive," White House press secretary Jay Carney said Friday. He said new sanctions would provide Iran an opportunity to argue that the United States negotiated in bad faith and would undermine American cooperation with partners it needs to enforce international sanctions on Iran.
Russia may already be negotiating a multibillion-dollar oil deal with Iran that would be hard for the United States to block, according to analysts who closely follow Iran. Despite their differences in other matters, Obama and Russian President Vladimir Putin have closely coordinated on nuclear nonproliferation matters. The U.S., Russia, Britain, China, France and Germany have been leading nuclear negotiations with Iran.
"I am very doubtful that Obama will take on Putin on this given his dependence on Russia ahead of the next round of nuclear negotiations," said Mark Dubowitz, an Iran expert at the Foundation for Defense of Democracies.
Separately, Republican Sens. Ted Cruz of Texas and Jim Inhofe of Oklahoma introduced their own bill this week designed to curtail the ability of the administration to engage in bilateral negotiations with Iran.
The Associated Press reported last year that much of the Nov. 24 nuclear deal resulted from a series of secret meetings between U.S. and Iranian officials. The key discussions took place in the Middle East sultanate of Oman and elsewhere over eight months.
But Cruz and Inhofe have asked the Senate Foreign Relations Committee to advance language conditioning any future U.S.-Iranian talks on the Islamic republic releasing any U.S. citizens being unjustly detained in its territory and affirming the "right of Israel to exist as a Jewish state." If such a requirement was applied universally, the United States would essentially have to end diplomatic relations with the entire Arab world and many other countries.
The legislation will almost surely be ignored by the committee, though Menendez's office declined to comment on its chances.