TEHRAN, May 6 (Xinhua) -- The fourth round of Iran-U.S. talks will be held in the Omani capital Muscat on Sunday, Nour News affiliated with the Iran's Supreme National Security Council quoted an informed official as saying on Tuesday.

The upcoming negotiations will center directly on humanitarian issues and certain security concerns of Iran and the United States, Nour News said.

The delegations of Iran and the United States, headed by Iranian Foreign Minister Seyed Abbas Araghchi and U.S. Special Envoy to the Middle East Steve Witkoff, have so far held three rounds of Oman-mediated talks on Tehran's nuclear program and the removal of Washington's sanctions. The first and third rounds were held in the Omani capital Muscat on April 12 and April 26, and the second one in Rome on April 19.

The fourth round, which was originally scheduled for May 3 in Rome, was postponed due to what Oman described as "logistical reasons."

Speaking at a weekly press conference in the Iranian capital Tehran on Tuesday, Iran's government spokesperson Fatemeh Mohajerani said Iran's red lines in the "indirect talks" with the United States are "fixed and clear."

"We will only talk about the nuclear issue and are committed to maintaining the red lines we have repeatedly mentioned in the past," she was quoted by Iran's official news agency IRNA as saying.

Iran considers nuclear energy necessary for achieving its peaceful purposes and meeting its energy needs, Mohajerani said, stressing that having access to nuclear energy is among the Iranian people's rights.

Iran has announced and proved in practice its commitment to the process of diplomacy, she said, calling on the United States to prove its positions.

Iran signed the 2015 nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), with six world powers -- Britain, China, France, Germany, Russia, and the United States. Under the deal, Tehran agreed to curb its nuclear program in exchange for sanctions relief.

The United States, led by President Donald Trump during his first term, unilaterally withdrew from the JCPOA in 2018 and reimposed sanctions, prompting Iran to gradually reduce compliance with its nuclear commitments. Efforts to revive the agreement have not achieved substantial progress.