Iran’s supreme leader has pushed back against U.S. criticism of the country’s nuclear program. Ayatollah Ali Khamenei said Tuesday that Tehran won’t seek permission from anyone to enrich uranium and called American statements “nonsense.

The comments by Iranian Foreign Minister Abbas Araghchi come after multiple rounds of talks between the two nations.

The dispute over uranium enrichment is the flashpoint in U.S.-Iran talks, with Tehran refusing to scale back and Washington warning of weaponization.