“The United States is refusing to rule out sanctions on India—a stated ally—if New Delhi goes through with a planned purchase of Russia’s new S-400 missile system this year, a top U.S. Defense Department official warned ahead of historic talks between the two countries next week. The S-400 ‘is a system that’s particularly troubling for a lot of reasons, and I think our strong preference … is to seek alternatives,’ said Randall Schriver, the U.S. assistant secretary of defense for Asian and Pacific security affairs, during an Aug. 29 event in Washington. ‘If they choose to go down that route, like I said, I can’t sit here and tell you today that the waiver will necessarily be used.’ The waiver Schriver referred to is a congressional loophole designed to insulate allies from ongoing U.S. sanctions against Russia.”
Source: Washington Warns of Sanctioning India Over Russian Missile System – Foreign Policy