Iran's supreme leader on Wednesday criticized an initial proposal from the United States in negotiations over Tehran's rapidly advancing nuclear program, though he stopped short of entirely rejecting the idea of agreement with Washington.

Iran's stance directly clashes with U.S. President Donald Trump 's position that Iran must halt all enrichment amid negotiations marked by uncertainty, despite having reached their most significant step since they began in April with a U.S. offer being delivered to Tehran last week.

An outline by the Trump administration would allow Iran to continue enriching uranium at low levels while a broader arrangement is worked out that would block the country’s path to a nuclear weapon.