U.S. Secretary of State John Kerry met Iranian Foreign Minister Mohammad Javad Zarif on Sunday even as President Barack Obama said that a “big gap” still remains between the two countries over a lasting nuclear deal, according to media reports. The U.S. and Iran are scheduled to hold a second day of high-level talks in Oman on Monday.

Kerry and Zarif held two meetings lasting over five hours in Muscat. Catherine Ashton, the former European Union foreign policy chief who is the lead negotiator in the talks, was also present, according to media reports.

“Talks between Kerry, Zarif and Ashton ... will continue on Monday, to narrow the gaps and reach a comprehensive deal by the Nov. 24 deadline,” IRNA, Iran’s official news agency, reported.

The meeting came on the day Obama expressed fears over the future of the nuclear talks, during an interview with CBS.

“The question now is are we going to be able to close this final gap so that they can reenter the international community, sanctions can be slowly reduced and we have verifiable, lock-tight assurances that they can't develop a nuclear weapon,” Obama said, during the interview. “There's still a big gap. We may not be able to get there.”

However, Youssef bin Alawi, the Omani foreign minister, seemed positive that a nuclear agreement could be hammered out before the Nov. 24 deadline, according to Reuters.

“By the level of commitment all parties are showing, we feel comfortable. There is no going back...I feel that all parties are positively willing to reach an agreement,” Alawi reportedly said after the talks.

Obama also reiterated that the U.S. will not be “connecting in any way” the nuclear talks with Iran to the fight against the Islamic State group in Iraq and Syria, CBS reported. Obama’s latest statements come just days after reports emerged that he had written a secret letter to Iran’s Supreme Leader Ayatollah Ali Khamenei urging cooperation in the fight against ISIS.

Following the second round of talks between Kerry and Zarif on Monday, delegates from the P5+1 nations -- U.K., China, France, Russia, the U.S. and Germany -- will meet in Muscat on Tuesday, before a final round of talks in Vienna on Nov. 18, according to media reports.