Republicans say it is up to Democrats whether new Iran sanctions pass the Senate to ensure Tehran sticks to a deal with the White House to open up its nuclear program to inspections.
Diplomats said Tuesday that the United Nations nuclear agency will convene a meeting Jan. 24 of the agency's leading nations on the deal reached between Tehran and six world powers - an agreement described Tuesday by Iran's president as representing the "surrender" of Western powers to his country's demands.
"Do you know what the Geneva agreement means? It means the surrender of the big powers before the great Iranian nation," Hassan Rouhani told a crowd in the oil-rich province of Khuzestan.
"The Geneva agreement means the wall of sanctions has broken. The unfair sanctions were imposed on the revered and peace-loving Iranian nation," he said. "It means an admission by the world of Iran's peaceful nuclear program."
Sen. John Barrasso, R-Wyo., says a bill to threaten harder sanctions on Iran has the votes to pass because of significant support from Democrats who want to keep the pressure on Iran to follow through on its commitments.
But Senate Majority Leader Harry Reid, D-Nev., has blocked the legislation - which has 59 co-sponsors including 43 Republicans and 16 Democrats - from coming to a vote at the White House's request.
White House spokesman Jay Carney said President Obama thinks the bill would anger Iranians and ruin a pact reached in November in Geneva.
Obama has threatened to veto the sanctions bill if is passes Congress but Barrasso says Democrats are backing it despite the threat.
"We'll continue to get additional support," Barrasso said. "You'd expect a number of the Democrat co-sponsors would force Harry's hand" to allow a vote.
The push for the bill comes as Iran agreed Sunday that an interim deal it agreed to will go into effect Jan. 20. The so-called Joint Plan of Action requires Iran to limit some of its nuclear activities for six months in return for about $7 billion in sanctions relief while more negotiations continue.
All but two Senate Republicans have expressed support for legislation that would increase sanctions in six months if the talks fail to achieve an agreement where Iran dismantles its industrial-scale centrifuge capacity and curtails suspected military components of its nuclear program.
Critics of the interim deal say its weaknesses mean more pressure is needed on Iran to get better results in future negotiations on a final deal. They say the deal should force Iran to dismantle its weapons capabilities such as centrifuges rather than accept its promise not to use that capability.
"There's nothing in this agreement that deals with militarization, weaponization, warheads," Barrasso said. "I worry that Iran will continue to develop in those areas as time ticks by."
Having additional sanctions in place will ensure that Iran and other countries that have agreed not to do business with Iran because of U.S. sanctions know "that six months from now, if the Iranians aren't in compliance, sanctions relief isn't going to go on forever," he said.
Iran's Deputy Foreign Minister Abbas Araghchi told Iranian state-TV on Sunday that while Iran's nuclear program is peaceful, Iran "will in no way, never, dismantle our centrifuges."
Under the interim deal, Iran must convert its stockpile of uranium that is close to bomb-grade to a harder to use form, but that process can be reversed "in one day," Araghchi said.
Not all Democrats are on board with the sanctions bill. Ten Democratic committee chairmen in the Senate said in a letter to Reid last month that they agreed that new sanctions now would "play into the hands" of Iranian hardliners who want negotiations to fail.
The White House has suggested Washington opponents want negotiations to fail so the United States can attack Iran.
"It's not clear why any member of Congress would support a bill that possibly closes the door on diplomacy and makes it more likely that the United States will have to choose between military options or allowing Iran's nuclear program to proceed," said Bernadette Meehan, a spokeswoman for the National Security Council.
Mark Dubowitz, executive director of the Foundation for Defense of Democracies, which has supported tougher sanctions on Iran, says it's a desire for improved chances for a negotiated solution and not war that motivates the Senate.
"You need enhanced negotiating leverage," to get the best results, he said.
Colin Kahl, who served as deputy assistant secretary of Defense for the Middle East during Obama's first term, said new U.S. sanctions could undermine Iranian pragmatists such as President Rouhani by demanding more than Iran may be willing to give up.
"I doubt more will hop on before hearing from Obama," he said.