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Sec. Kerry: "We will not rush" Iran nuclear deal

After several delays in meeting self-imposed deadlines to hammer out a nuclear agreement with Iran, Secretary of State John Kerry said Wednesday that negotiators won't rush a deal -- though the U.S. wasn't willing to "sit at the negotiating table forever."

"Given that the work here is very technical and that the stakes are very, very high, we will not rush and we will not be rushed," Kerry said Wednesday in Vienna, where negotiations are taking place among six world powers and Iran. "But as I have said many times -- and as I discussed with President Obama last night -- we are not going to sit at the negotiating table forever. We also recognize that we shouldn't get up and leave simply because the clock strikes midnight."

Iran nuclear talks deadline extended again

If negotiations drag on past Thursday, it could mean extra time for Congress to appraise and approve the deal. According to the Iran Nuclear Agreement Review Act passed in May, if the president sends a deal for Congress to evaluate after July 9, the deliberative body can take as long as 60 days -- as opposed to the previously required 30 -- to review it. Though legislators can't stop the U.S. from implementing the entirety of the deal, they can block the administration from lifting certain sanctions imposed by Congress in the first place.

According to CBS News correspondent Margaret Brennan, Kerry is poised to remain in Vienna until Friday, but that his team is still hoping to get a deal signed for Congress to review by Thursday.

"This is not open ended," Kerry told reporters Thursday. "President Obama made it very clear to me last night. You can't wait forever for a decision to be made. We know that. If the tough decisions don't get made, we are absolutely prepared to call an end to this process."

Iran's Foreign Minister, Javad Zarif, also took to Twitter early Thursday to say that the negotiations were "not rushed."

We're working hard, but not rushed, to get the job done. Mark my words; you can't change horses in the middle of a stream. #IranTalksVienna

— Javad Zarif (@JZarif) July 9, 2015

Some members of Congress are signaling that a slow approach to the negotiations will make for a better overall deal.

Sen. Bob Corker, R-Tennessee, said Thursday that he was "glad they are taking their time."

"I would much rather they take time on the remaining issues and make sure they do the very best they can to get them as good as they can," the Senate Foreign Relations Committee chair told CBS News. "I'd rather they delay than end up in making what's been a very downward trend the last couple of months even more downwardly trending. So I'm glad they are taking their time."

The committee's ranking Democrat also added his support for Kerry and his team.

"We want him to take as much time as he needs, within reason," Sen. Ben Cardin, D-Maryland, said Thursday. "As he pointed out there is not an unlimited amount of patience here. As long as there is a reasonable path forward, we want him to take the time to get the right agreement. And if it can't be done , we have to know soon."

The existing freeze on Iran's nuclear program is scheduled to expire Friday, July 10. Iranian diplomats say they could conceivably agree to roll that over for the duration of the ongoing talks.

There has been a breakthrough on guaranteeing weapons inspectors access to suspect nuclear sites including those on military installations, one of the outstanding issues where the parties had major disagreements. However, there are still issues disputes about how quickly Iran will be able to ramp up enrichment after a decade-long freeze and how much development of advanced centrifuges it can continue during the agreement. The Iranian negotiators also want the U.N. sanctions lifted including an embargo on missiles and conventional weapons.

"All that we are focused on is the quality of the agreement and that is what will continue to define our work," Kerry said.

CBS News' John Nolen contributed to this report.