Vice President Joe Biden, Secretary of State John Kerry and Treasury Secretary Jack Lew planned to meet with the Senate Democratic leadership and members of the Senate Banking Committee tomorrow in hopes of convincing lawmakers to delay plans to meet next week and draft a new package of penalties.
Although the White House insists that tough sanctions have forced Iran to negotiate, it want Congress to pause in imposing new, punitive measures to give negotiators flexibility in talks with Iran. Lawmakers argue that this is no time to let up on Tehran.
Unnerving for the administration is the prospect that a Senate panel would be crafting new sanctions at the same time as Iran and six world powers meet in Geneva next week for another round of negotiations.
Western powers have been trying to determine Iran's seriousness in complying with demands it prove its nuclear programme is peaceful since reformist President Hassan Rouhani took office in August. Both sides described their last round of talks as positive, with Tehran ready to discuss some curbs on programmes that can create both atomic energy and the fissile core of nuclear arms.
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The Senate bill may narrow that time frame, block international investment in more economic sectors, try to close off Iran's foreign accounts and tighten President Barack Obama's ability to waive requirements for allies and key trading partners who continue to do business with Iran.
Administration officials met last week with Senate staffers and made their case to some American Jewish groups during a White House meeting earlier this week.