US lawmakers are preparing a possible vote on new sanctions against Iran, a move President Barack Obama and his P5+1 partners fear could sabotage the nuclear deal reached in Geneva.

Administration officials have beaten a path to Capitol Hill in recent weeks, warning Congress against short-circuiting the delicate negotiations.

Now that the talks have borne fruit in the form of an interim accord on Tehran's nuclear program, officials are again encouraging a go-slow approach by lawmakers to allow the parties to reach a final deal.

But the public and private lobbying has not deterred many in Congress who are determined to tighten the noose on Iran's oil sector and industries like mining, construction and engineering.

They say sanctions are what brought Tehran to the negotiating table, and escalating the penalties is the only effective mechanism to push Tehran toward a comprehensive agreement.

Iran and the P5+1 group -- Britain, China, France, Russia and the United States plus Germany -- reached a landmark deal in Geneva on November 24 on the Islamic republic's disputed nuclear drive that the West suspects has military dimensions, despite Tehran's denial.

But even as the six-month Geneva agreement provides for partial suspension of existing sanctions, a bipartisan group of senators led by Senate Foreign Affairs Committee Chairman Robert Menendez, a Democrat, and Republican Senator Mark Kirk were set to unveil a sanctions bill.

The text would serve as a stick of sorts "if the regime cheats on the interim deal or tries to drag out negotiations on a final deal," said one Senate aide involved in the sanctions discussions.

"The senators remain hopeful a deal can be reached this week in time to put something on the president's desk by Christmas."

The timing or legislative vehicle for the text depend on a decision by Senate Majority Leader Harry Reid, who last month expressed support for introducing new sanctions legislation but hasn't said whether he will allow a vote next week.

Another Senate aide said that at the end of the interim period, a clause could allow Obama to briefly postpone implementation of the additional sanctions, provided that a final agreement proved to be imminent.

"I think creating a sanctions regime that is an insurance policy and also creates leverage for us (in negotiations) is incredibly important," Menendez told CBS television's "Face the Nation."

The penalties, if imposed, could again lower the authorized ceiling of Iranian oil exports, currently about 1.2 million barrels per day, further strangling the regime's economic lifeblood.

The six countries still importing Iranian oil -- and currently exempt from US sanctions -- could face penalties if they do not reduce import volumes within a specified period.

Kerry due to testify in Congress

Congress has played "bad cop" for years against the diplomatic efforts by Obama, who has had little sway on lawmakers on Iran.

Highlighting the eagerness for congressional action, the House of Representatives passed tough Iran sanctions in July by a vote of 400-20. In the Senate, the three sanctions bills adopted since 2010 passed unanimously.

Obama can veto any legislation, but if the new sanctions were included in a broader defense spending bill this month, as some expect, a veto would be playing with political fire.

Hawks see Iran wanting to keep all players negotiating as long as possible to benefit from the easing of sanctions.

"The longer they keep the P5+1 at the table, the more money they'll generate, and the more money they'll generate, the less negotiating leverage the P5+1 will have," said Mark Dubowitz, an expert from the Foundation for Defense of Democracies who supports tougher sanctions.

Like the White House, the P5+1 group is watching Congress's next moves closely.

"For us it's a parameter of course. By definition, we have very little influence on that," a senior Western official told AFP.

Senators return to Washington on Monday, for a decisive week.

If the Democratic leadership opts against putting sanctions to a vote soon, sanction supporters could try to force their hand, for example through House legislation.

In a final plea, Secretary of State John Kerry testifies before a House panel Tuesday in a bid to head off new punitive measures.