The killing of an American citizen during a protest last week in Israeli-occupied West Bank was "unprovoked and unjustified" and shows that the Israeli security forces need to make some fundamental changes in their rules of engagement, U.S. Secretary of State Antony Blinken said Monday.

"No one should be shot and killed for attending a protest," Blinken told a news conference in London, delivering his harshest comments to date against the Israeli military.

"In our judgment, Israeli security forces need to make some fundamental changes in the way that they operate in the West Bank, including changes to their rules of engagement," he said.

Aysenur Ezgi Eygi, a 26-year-old activist from Seattle who also held Turkish citizenship, was killed Friday after a demonstration against Israeli settlements in the occupied West Bank, according to Jonathan Pollak, an Israeli protester who witnessed the shooting.