A new non-partisan report by top foreign policy experts largely backs White House warnings that imposing new sanctions on Iran could seriously complicate, if not derail, hopes of a final nuclear deal with Tehran.

The study by the Iran Project assesses claims by critics of the sanctions push in Congress that it would fracture the international coalition pursuing talks -- which resumed in Austria on Tuesday -- and a sanctions regime already squeezing Iran's economy.

But it also argues that the Obama administration has been a little too adamant that the bill, if passed, would inevitably lead to war with the Islamic Republic.

The White House, has for now, succeeded in thwarting a bid by a bi-partisan group of hawkish senators to pass new sanctions on Iran which they say will increase US leverage in nuclear talks.

Supporters of the legislation, including the Democratic leader of the Senate Foreign Relations Committee Robert Menendez, say that any new sanctions would only come into force in a "trigger" mechanism in six months if talks on a permanent nuclear deal fail.

But the Iran Group report casts doubt on that claim, an important point because Washington promised not to impose new sanctions in an interim deal with Iran reached late last year.

"After carefully reading the bill line by line and consulting with both current and retired Senate staff of the relevant committees, it appears that the critics are correct: the change in sanctions law takes effect upon passage," the report said.

The report questions the claim by pro-sanctions supporters that since economic pain brought Iran to the table, more punishment will get it to capitulate in negotiations.

"Medicine administered at a certain dosage can improve the health of a patient, but if that patient turns around and doubles it, they might poison themselves."

The report also supports the contention that imposing new sanctions in Washington could undermine President Hassan Rouhani among ultra hard liners in Tehran.

It gives some credence to the idea that US allies would see the imposition of new sanctions by Congress as a failure by Washington to live up to its promises.

But the administration got little support for its claims that the sanctions bill could put the United States on a "march to war" with Iran, by killing off chances of a diplomatic solution.

"It would seem that both sides are too confident in their claims that a new sanctions bill will lead directly to war or that the Iranians will never walk away," the report said.

Still, it concluded that the new sanctions bill could increase the probability of war with Iran even if it did not guarantee such an outcome.

The report was written by Jim Walsh, a researcher at the Massachusetts Institute of Technology and included contributions from foreign policy experts including career diplomat Thomas Pickering, former senior CIA officer Paul Pillar, and Jessica Tuchman Matthews, president of the Carnegie Endowment for International Peace.