A group of Democratic and Republican senators introduced the bill to impose tighter U.S. sanctions on Iran over ballistic missile launches and other non-nuclear activities.
Tehran's top nuclear negotiator hopes diplomacy resuming this week will yield results before a self-imposed deadline for a final deal to curtail Iran's atomic program expires at the end of June.
"I neither support nor oppose the deal. Everything is in the details, it may be that the deceptive other side wants to restrict us in the details," Khamenei said in a speech broadcast live on state television.