Senate Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., on Friday said she would oppose efforts to pass additional sanctions on Iran as the administration works to broker a deal on Tehran's nuclear program.

“I strongly oppose any attempt to increase sanctions against Iran while P5+1 negotiations are ongoing,” she said in a statement.

The support of Feinstein could be critical to the White House's effort to convince lawmakers to hold off on new sanctions.

“The purpose of sanctions was to bring Iran to the negotiating table, and they have succeeded in doing so. Tacking new sanctions onto the defense authorization bill or any other legislation would not lead to a better deal. It would lead to no deal at all,” Feinstein continued.

“I am baffled by the insistence of some senators to undermine the P5+1 talks. I will continue to support these negotiations and oppose any new sanctions as long as we are making progress toward a genuine solution,” she added.

The international community has imposed tough sanctions on Iran over fears it is developing nuclear weapons, but Tehran insists its program is for peaceful purposes only. The P5+1 group, consisting of the U.S., United Kingdom, France, Germany, Russia and China is negotiating with Tehran over its nuclear program.

The Obama administration is seeking a diplomatic deal with Iran which would offer temporary limited sanctions relief in exchange for Tehran freezing some aspects of its nuclear program.

That deal though is facing tough opposition on Capitol Hill, where lawmakers fear the Obama administration is undermining the international sanctions regime. Key U.S. allies, including Israel and France, have also expressed skepticism.

Some lawmakers led by Sen. Lindsey Graham, R-S.C., are weighing additional sanctions to further tighten pressure on Tehran. But the Obama administration has urged Congress to allow more time for diplomacy to work.

The administration has launched a full court press to convince lawmakers to hold off on another round of sanctions, with Vice President Joe Biden speaking to senators and Secretary of State John Kerry briefing the Senate Banking Committee about the Iran talks.

CNN reported earlier Friday that an official familiar with the negotiations said both sides were “getting close” to a deal.

Obama on Thursday publicly defended his diplomatic push, saying that the U.S. would lose “nothing” by negotiating with Iran.

He said his proposed deal would leave the “entire sanctions infrastructure still in place.”

“If we're serious about pursuing diplomacy, there's no need for us to add new sanctions,” Obama added.

White House correspondent Susan Crabtree contributed to this story.