Congressional support for a new round of sanctions against Iran is growing, with a near filibuster-proof majority of senators now willing to approve fresh legislation, according to senior Senate aides.

There are no plans for Senate Majority Leader Harry M. Reid (D-Nev.) to allow a vote on any proposal in the near future, the aides said, but if a bill moves forward, it could complicate negotiations with Iran over its nuclear program.

The Obama administration has urged lawmakers not to impose new sanctions while the U.S. and five other world powers negotiate with Iran on a permanent deal to ensure that it cannot develop nuclear weapons. Two months ago, Iran agreed to freeze its nuclear program in exchange for temporary relief on some sanctions.

On Friday, Iran’s top nuclear envoy signaled that the text of an initial agreement was being circulated among the negotiating countries for further approval. In Geneva, Abbas Araghchi, Iran’s top nuclear envoy, told the official IRNA news agency that he expected countries to respond within two days about whether they accept the terms of an interim agreement; it would map out a six-month plan to be implemented while diplomats continue negotiating any final deal.

The White House fears that further sanctions could scuttle the temporary accord. But congressional support for imposing more sanctions remains strong and Sens. Robert Menendez (D-N.J.) and Mark Kirk (R-Ill.) have introduced a proposal to impose a new round of sanctions that would be applied if Iran backed away from an agreement. The measure would put further restrictions on Iran’s fuel purchases and certain sectors of the country’s economy.

Menendez, who chairs the Senate Foreign Relations Committee, and Kirk introduced the proposal late last year with 25 co-sponsors. On Thursday, Senate Minority Leader Mitch McConnell (R-Ky.) and Sens. Thad Cochran (R-Miss.), Mike Crapo (R-Idaho) and Richard C. Shelby (R-Ala.) joined a growing list of co-sponsors that numbered at least 59 by Friday afternoon, according to official Senate records of pending legislation.

Another Senate aide familiar with the talks said that a less formal tally has support among senators “in the mid-70s.”

Senate procedural rules require at least 60 votes to help end debate on legislation.

In an op-ed in The Washington Post on Friday, Menendez wrote that a diplomatic agreement that ends Iran’s nuclear weapons program remains his preferred result, but “backing up this achievement by taking out a diplomatic insurance policy is an act of reasonable pragmatism.”

Reid has avoided taking a public position on the issue and has not signaled whether a vote will be permitted. For weeks he has dodged questions about the topic, usually telling reporters to “check with Menendez on that.”