In a sign of hope for diplomacy over war, the U.S. and Iran began engaging in serious, high level negotiations over Iran’s civilian nuclear program in April for the first time since President Donald Trump pulled the U.

Iran’s supreme leader has denounced a proposal by the United States aimed at curbing Tehran’s nuclear efforts and demanded that his country retains national independence amid reports of Washington offering to become involved in Tehran’s nuclear program.

Iranian, Egyptian and U.N. leaders have met to discuss Iran’s nuclear program after the U.N. nuclear watchdog agency said Iran is increasing its stockpile of uranium enriched to near weapons-grade levels.