TEHRAN, May 11 (Xinhua) -- Iranian Foreign Minister Abbas Araghchi said on Sunday that indirect negotiations with the United States in Oman to revive the 2015 nuclear deal had become "much more serious and frank," as President Masoud Pezeshkian rejected U.S. demands for Tehran to dismantle its nuclear infrastructure.

The talks in Muscat, facilitated by Oman, mark the latest effort to salvage the Joint Comprehensive Plan of Action. The United States unilaterally withdrew from the accord in 2018 under U.S. President Donald Trump's first term, prompting Iran to reduce compliance with its nuclear commitments gradually.

Araqchi, speaking to Iran's state-run IRIB TV after the fourth round of negotiations in Oman's capital, said the discussions had shifted from general topics to more specific proposals. He characterized the talks as "forward-moving" but acknowledged the growing complexity of the issues. Both sides agreed to continue the discussions.

The latest round, lasting about three hours, follows previous sessions in Muscat on April 12 and 26, and in Rome on April 19.

Meanwhile, President Pezeshkian firmly rejected U.S. calls to dismantle Iran's nuclear infrastructure. "This is unacceptable. Iran will not relinquish its peaceful nuclear rights," he declared, reaffirming Tehran's stance that its nuclear program is for civilian purposes. He also referenced a religious decree from Supreme Leader Ali Khamenei banning nuclear weapons development.

Ahead of the Muscat talks, U.S. Special Envoy Steve Witkoff reiterated demands for Iran to completely dismantle its nuclear program, including facilities at Natanz, Fordow, and Isfahan. U.S. officials, including Secretary of State Marco Rubio, have suggested that Iran should import enriched uranium.

Pezeshkian stressed that Iran's nuclear activities are essential for "peaceful" purposes, such as radiopharmaceuticals, healthcare, agriculture, and industry. "We are serious in the negotiations and seek an agreement. We hold talks because we want peace," he said, emphasizing Iran's commitment to regional peace and security.