WASHINGTON - Legislation to impose tough new sanctions on Iran is not expected to come to a vote in the Senate before December, after the end of the next round of negotiations over Tehran's nuclear program, US lawmakers and congressional aides said on Monday.As diplomats headed to Geneva for a third round of talks this week, members of Congress have been debating behind closed doors whether to go ahead with the new set of stricter economic sanctions on Iran relating to its nuclear program. President Barack Obama has asked Congress to hold off on more sanctions to allow time to pursue a diplomatic deal.The Senate Banking Committee, which had been expected to vote on a stand-alone sanctions bill by September, delayed such action at the Obama administration's request.Frustrated by the committee's failure to move ahead, several Republicans have said they were considering proposing new sanctions on Iran as an amendment to a defense authorization bill the Senate is debating this week.But lawmakers and aides said on Monday no such action was expected until after senators come back on Dec. 2 from next week's Thanksgiving recess."I don't see anything happening until we get back," Senator Bob Corker, the top Republican on the Senate Foreign Relations Committee and a Banking Committee member, told reporters.Democratic Senator Tim Johnson, the banking panel's chairman, declined comment on when the committee might consider the stand-alone sanctions package.The White House said Obama would meet with senators from both parties on Tuesday to try to convince them not to adopt further sanctions now. The session follows briefings for members of Congress by Vice President Joe Biden, Secretary of State John Kerry and other officials.Iran sanctions are a rare area where US Republicans and Democrats work together. US lawmakers, including many of Obama's fellow Democrats, are generally more hawkish on Iran than the administration.Supported by the influential pro-Israel lobby, measures condemning Iran generally pass both houses of Congress by overwhelming margins. The Republican-controlled House of Representatives approved its tighter sanctions bill in July by a vote of 400 to 20. The Senate is controlled by Democrats.Corker said he still thinks there will be some attempt by Democratic and Republican senators to add an Iran sanctions amendment to the defense legislation, known as the National Defense Authorization Act (NDAA), although it would reflect the outcome of the Geneva talks."I do think there will be a bipartisan attempt to put something on NDAA relative to Iran, but obviously if negotiations conclude it will be different than what it would have been beforehand," he said.The United States and five other nations are negotiating a proposal that would ease economic sanctions imposed on Iran if it suspends some parts of a program that many countries, particularly in the West, fear is aimed at developing a nuclear weapons capability.Ahead of continued talks over Iran's nuclear program this week in Geneva, US Secretary of State John Kerry on Monday pressed Iran to finalize an agreement that can prove to the world its nuclear program is peaceful, but said he has "no specific expectations" for the coming round of negotiations."I have no specific expectations with respect to the negotiation in Geneva except that we will negotiate in good faith and we will try to get a first-step agreement," Kerry told a news conference with Turkish Foreign Minister Ahmet Davutoglu.Kerry said he hoped that "Iran will understand the importance of coming there prepared to create a document that can prove to the world this is a peaceful program.""I am not going to negotiate this in public. We all need to be respectful of each others' processes here and positions - and so it's best to leave that negotiation to the negotiating table," he added, declining to discuss details of a proposal under discussion.Iran has denied that it wants to develop atomic weapons capability, saying its nuclear program is limited to the peaceful generation of electricity and other civilian uses.