Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif were both optimistic Wednesday after several hours of "substantive" talks aimed at ending an impasse over limits to Iran's nuclear program.

But time may be running out on a deal.

Supporters of new sanctions in Congress are gearing up for action, prodded by what they see as new provocations from Iran, such as the referral Wednesday of Washington Post reporter Jason Rezaian for prosecution by a revolutionary court and Iranian President Hassan Rouhani's announcement the day before that his government is building two new nuclear power plants in the southern province of Bushehr.

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The Obama administration, meanwhile, continues to tolerate Iranian provocations to keep the talks going, leading some lawmakers to say it's time to give up on them altogether.

"What started as an unwise policy has now descended into a dangerous farce," freshman GOP Sen. Tom Cotton of Arkansas said Tuesday in a speech at the Heritage Foundation.

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"Iran's achieving through slow motion all that it might want in a final deal," he said. "It's time for the responsible adults in both parties in the Congress to stop this farce."

Kerry and Zarif were meeting to see if talks can be concluded on a final deal before the deadline to replace a November 2013 interim deal is missed for a third time. Negotiators hope to have the framework for a permanent deal in place by March and finalize it before the extension runs out June 30.

After the two men met in Geneva, Zarif told reporters the discussion had been "important," adding: "I think it will show the readiness of the two parties to move forward to speed up the process."

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The volume of Iran’s uranium enrichment activities, the timetable for removal of sanctions and the deadline for reaching a final deal are the main sticking points in the talks, according to Iran's official Islamic Republic News Agency.

Meanwhile, in Washington, State Department spokeswoman Marie Harf defended the process against congressional criticism.

"This administration’s policy has led to a place where Iran’s nuclear program is frozen for the first time in a decade," she told reporters. "The diplomacy we’ve put in place has led to that happening and that outcome, and has led to us negotiating whether we can prevent Iran from getting a nuclear weapon through diplomacy, which I think many people, most people agree is the most durable, best way to do so."

But the administration's arguments are losing ground on Capitol Hill, as Iranian officials warn that new sanctions would bring a halt to the talks. Instead there's a growing sentiment that the administration has lost the leverage it needs to reach a deal that would prevent Iran from being able to build a nuclear weapon, let alone secure the release of detained Americans such as Rezaian, who has been held since July, or end Iran's support for terrorism.

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Sens. Robert Menendez, D-N.J., and Mark Kirk, R-Ill., are expected to soon introduce a version of their sanctions bill that was blocked last year by then-Senate Majority Leader Harry Reid, D-Nev. Rep. Eliot Engel of New York, the top Democrat on the House Foreign Affairs Committee, told Al-Monitor he and Chairman Ed Royce of California have begun work on their own sanctions legislation.

Meanwhile, the Senate Banking Committee has scheduled a Jan. 20 hearing on "perspectives on the strategic necessity of Iran sanctions."

Because of the entrenched opposition to its negotiating posture, the administration has hinted it might bypass Congress in implementing a final deal, which both Cotton and Senate Armed Services Committee Chairman John McCain, R-Ariz., said lawmakers would not allow.

"The only brake on this administration, in my view, from giving away the store is the belief that [an agreement] has to go through Congress," McCain said.