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NEW: Negotiations with Iran extended to July 7, a U.S. State Department official said Tuesday

NEW: Tuesday had been Iran's self-imposed deadline to reach a deal with the six world powers

(CNN) —  

Negotiations with Iran over nuclear capability have been extended to July 7, a U.S. State Department official said Tuesday.

Tuesday had been Iran’s self-imposed deadline to reach a deal with the six world powers (including the U.S.) with whom it is negotiating the future of its nuclear program.

That group called the P5+1 nations, and Iran have decided to allow more time for negotiations to reach a long-term solution on the Iran nuclear issue, State Department spokeswoman Marie Harf announced in an email.

Returning to Vienna for the final stretch of nuclear negotiations after getting instructions from Tehran, Iranian Foreign Minister Mohammad Javad Zarif said Tuesday he was looking to seal a final deal.

“I’m here to get a final deal and I think we can,” Zarif said.

Zarif’s comments came as he emerged from a meeting Tuesday morning with Secretary of State John Kerry that lasted more than an hour.

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Negotiators were not expected to reach a final deal by the end of the day, though, instead aiming to broker a final deal to curb Iran’s nuclear program for at least 15 years by July 9 – the deadline Congress has imposed to keep its review period to 30 instead of a lengthy 60 days.

The White House is hoping to achieve a deal by the ninth to avoid a lengthy political battle in Washington that could skew public opinion – and votes in Congress – against an eventual deal.

Republicans in Congress are warning that the Obama administration is preparing to broker a bad deal, one they say would not have sufficient checks on Iran’s nuclear program and could threaten the safety of the U.S.’s top ally in the Middle East, Israel.

After the review period, Congress will vote to either approve or disapprove of an eventual nuclear agreement with Iran. But Republicans would need to rally more than a dozen Democrats to override President Barack Obama’s veto in order to reject a deal – no easy feat.

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