MUSCAT, oman — The Obama administration is facing its last best chance to curb Iran’s nuclear program, not just to meet an end-of-the-month deadline for a deal but also to seal one before skeptical Republicans who will control Congress next year are able to scuttle it.

Years of negotiations to limit Iran’s nuclear production entered the final stretch Sunday as U.S. Secretary of State John Kerry met with Iranian Foreign Minister Javad Zarif and European Union senior adviser Catherine Ashton in Oman’s capital.

Officials said the discussions were expected to continue into Monday.

The stakes are high as the Nov. 24 deadline approaches. A deal could quell Mideast fears about Iran’s ability to build a nuclear bomb and help revive the Islamic Republic’s economy.

It also would deliver a foreign policy triumph for the White House, which is being hammered by prominent Republican senators over its handling of the civil war in Syria and the growth of the Islamic State militancy in Iraq. Those same critics seek to put the brakes on U.S.-Iranian bartering once they take the majority Jan. 3.

President Barack Obama said Sunday on CBS’s “Face The Nation” that his administration’s “unprecedented sanctions” on Iran are what forced Iran to the negotiating table.

But Obama also cited “a big gap” between Iran and world powers as they try for a final agreement. “We may not be able to get there,” he said in the interview broadcast Sunday.