Iran has slowed the pace at which it is enriching uranium to nearly weapons-grade levels, according to a report by the United Nations’ nuclear watchdog seen by The Associated Press on Monday. That could be a sign Tehran is trying to ease tensions after years of strain between it and the U.S.

The confidential report comes as Iran and the United States are negotiating a prisoner swap and the release of billions of dollars in Iranian assets frozen in South Korea. However, international inspectors also noted new challenges in trying to monitor Iran’s program.