Former U.S. Secretary of State Hillary Clinton is urging Congress to resist imposing new sanctions on Iran over its nuclear program, saying that "this is the time" to give diplomacy a chance to work.

Clinton, who leads the pack among potential Democratic presidential contenders for 2016, according to Reuters polling, said in a January 26 letter to Democratic Senator Carl Levin, "Now that serious negotiations are finally under way, we should do everything we can to test whether they can advance a permanent solution."

?Hillary Clinton [file photo]

Her comments came after Levin wrote to her about the sanctions issue. The lawmaker released her letter on Sunday.

Fifty-nine of the 100 U.S. senators, including 16 of President Barack Obama's fellow Democrats, co-sponsored a bill that would impose new restrictions on Iran if talks on a permanent deal falter.

Iran, which insists its atomic ambitions are limited to peaceful purposes, has warned it will walk away from negotiations on its nuclear program if the bill becomes law. The measure is now stalled in the Senate amid expectations the chamber's Democratic leaders will not allow a vote.

Obama pledged in his annual State of the Union address last week to veto any legislation that threatens talks with Tehran. He said an interim agreement seeking to curb Iran's nuclear program was already taking effect, and the ongoing diplomacy between Iran and six world powers was important for U.S. safety.

Noting she was a longtime supporter of previous sanctions against Iran, Clinton told Levin that she shared his position that those measures "and the carefully constructed global consensus behind them are responsible for driving Tehran to the negotiating table."

She said that like Obama, she had no illusions about the ease or likelihood of reaching a permanent deal with Iran, "yet I have no doubt that this is the time to give our diplomacy the space to work.

"If it does not, there will be time to put in place additional sanctions in the future, with greater international support necessary to ensure enforcement, and to explore every other option on the table," she wrote.