Vice President Joe Biden and senior Obama administration officials convinced a number of senators to hold off on another round of Iran sanctions as Western powers test Tehran's willingness to scale back its nuclear aims.

The pressure Thursday didn't sway every senator who participated in the hours-long, closed-door briefing, but the chances that the Senate Banking Committee would draft new, punitive measures next week just as negotiations occurred in Geneva diminished significantly.

White House spokesman Jay Carney said President Barack Obama is not seeking an open-ended delay to new sanctions and believes there may come a point where additional economic penalties against Iran are necessary. Kerry told senators that the president wants to keep the current sanctions regime in place while negotiating with Iran.

Western powers have been trying to determine Iran's seriousness in complying with demands it prove its nuclear program is peaceful since reformist President Hassan Rouhani took office in August. Both sides described their last round of negotiations as positive, with Tehran ready to discuss some curbs on programs that can create both atomic energy and the fissile core of nuclear arms.

Republican Sen. Dean Heller said the administration was "making a good case" for delaying another round of penalties although he said he had not made a decision.

Joining Biden in the discussions with Democratic leadership and committee members were Secretary of State John Kerry and Treasury Secretary Jack Lew, a lineup that underscored the administration's strong desire to get Congress to wait on a new package of penalties. Although the White House insists that tough sanctions have forced Iran to negotiate, it wants Congress to pause to give negotiators flexibility in talks with Iran.

"I like John Kerry, I got a lot of trust in John Kerry," said Democratic Sen. Jon Tester, who explained that it might make sense for the committee to wait, finalize any legislation "and let them (the administration and Western powers) do their negotiations."

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.

The chairman of the Banking committee, Democratic Sen. Tim Johnson said he was undecided on whether the panel would craft the bill next week. Republican and Democratic congressional aides indicated that it was unlikely on the same days as the international talks.

Several lawmakers emerging from the session argued that this is no time to let up on Tehran.

"I have to hear something far more substantive to dissuade me from being an advocate for pursuing a new round of sanctions," said Democratic Sen. Bob Menendez, chairman of the Foreign Relations Committee who has repeatedly sponsored tough sanctions legislation.

Republican Sen. Mark Kirk, who has often partnered with Menendez, said his response to the administration's intense lobbying was to keep pushing for sanctions.

"I think we need to keep rolling with the pressure," Kirk said. "Without sanctions, you have war. Sanctions are the only way to prevent a war. I don't want to condemn our allies and Israel to a war."

The Banking Committee is weighing a bill that would blacklist Iran's mining and construction sectors. It largely mirrors a House measure that passed overwhelmingly by a 400-20 vote in July. That bill also called for all Iranian oil sales to end by 2015.

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 Obama's ability to waive requirements for allies and key trading partners who continue to do business with Iran.

The powerful American Israel Public Affairs Committee, which has considerable sway in Congress, favors more sanctions to stop Iran.

Even if the administration succeeds in convincing Democratic leaders and Johnson to delay a vote, Kirk said he would try to attach new sanctions to the annual defense policy bill that the Senate could consider as early as the week of Nov. 12.

"I would look for every opportunity as a senator," he said.