WASHINGTON (Reuters) - The United States is preparing further sanctions over killings of anti-government protesters in Iraq, a senior U.S. State Department official said on Friday.

“We’re not done. This is an ongoing process,” David Schenker, an assistant secretary at the State Department, told reporters, adding later: “We will be doing further designations in the future.” He did not provide further details.

Earlier on Friday, the United States blacklisted three Iran-backed Iraqi paramilitary leaders over their alleged role in the killings. The groups deny any role in the protesters’ deaths.