The United States is 'encouraged' by the results of the fourth nuclear talks with Iran; a meeting will be held next.

A senior U.S. official on Sunday welcomed the results of the fourth round of negotiations with Iran over its nuclear program and announced that another meeting will be held soon.

"An agreement was reached to advance the talks and continue working on technical elements. We are encouraged by today's outcome and look forward to our next meeting," the senior official said, speaking on condition of anonymity.

The talks in Oman, led by U.S. special envoy Steve Witkoff and Iranian Foreign Minister Abbas Araqchi, "were again direct and indirect, lasting more than three hours," the source said.

For its part, Iran described the meetings as "difficult."

"The fourth round of Iran-US indirect negotiations has concluded; difficult but useful talks aimed at better understanding each other's positions and finding reasonable and realistic ways to address differences," Foreign Ministry spokesman Esmaeil Baqaei said in X.

Prior to the meeting, the Iranian foreign minister said he hoped this round of talks with the United States would reach a "decisive moment."

Without diplomatic relations since 1980, Iran and the United States have held three sessions of talks mediated by Oman since April 12 on the thorny issue of Iran's nuclear program.

The goal of the meetings is to conclude a new agreement to prevent Iran from acquiring nuclear weapons in exchange for the lifting of the numerous sanctions that paralyze its economy.

Tehran maintains that its aims are exclusively civilian, although the United States and other Western countries fear that it is seeking to develop an atomic weapon and warn that it is approaching the level of uranium enrichment necessary for this.