Republican senators are demanding the escalation of sanctions against Iran after two days of nuclear talks in Geneva.
Sen. Mark Kirk says Iran's refusal to halt its "nuclear and ballistic missile programs" means the Senate should immediately target all Iranian government revenue and reserves.
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The Senate Banking Committee is expected to draft new sanctions soon, mirroring a House bill passed in July. That bill blacklisted Iran's mining and construction sectors and called for all Iranian oil sales to end by 2015. The Senate's bill may narrow that time frame.
The Geneva talks ended upbeat Wednesday, with new talks set for November.
Sen. Marco Rubio was also unimpressed, issuing a resolution calling for more sanctions.
Lawmakers including Robert Menendez, the chairman of the Senate Foreign Relations Committee, have signaled they want Tehran to stop even low-level enrichment of uranium used in generating power before they would take steps to wind down existing sanctions, or even agree not to put through tougher ones.
"Sanctions relief is easier said than done," said Ali Vaez, an Iran analyst at the International Crisis Group, an organization that seeks to prevent and resolve conflict.
"Without a fundamental reorientation of Iran's approach, a significant relaxation in sanctions is not in the cards."
The sanctions Washington would likely wind down first are morsels such as easing restrictions on medical supplies, travel and the sale of spare airplane parts and service for US-built aircraft in Iran.
"Many of these are low impact, they are not going to turn Iran's economy around," said Greg Theilmann, a fellow at the Arms Control Association, and a former top intelligence official at the State Department.
"But it's important to at least know there are a number of things that can be done to show US bona fides if the Iranians show that they are willing to take significant steps in the direction of what the US and other parties say they have to do," he said.
A congressional aide suggested freezes that have been placed on Iran's property and bank accounts in the United States and around the world - estimated to be worth tens of billions of dollars - and sanctions on oil transactions could be relaxed in stages over many months, if Iran were to make verified major concessions.
"Iran is going to want ... some sort of relief on the obstacles that we've put in the way of oil transactions and oil revenue, access to their reserves that they have on deposit outside the country and to the revenues that they've already earned that are now blocked," the aide said. "You can calibrate it all kinds of different ways," in stages, he added.
AP and Reuters contributed to this report
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