Turkey’s fraught relations with the United States are heading for further turbulence after a grand jury in Washington indicted 15 Turkish security officials accused of attacking pro-Kurdish protesters in the US capital on May 16 during a visit by Turkish President Recep Tayyip Erdogan. They include Muhsin Kose, the head of Erdogan’s security detail. In all, 19 people who engaged in acts of violence against the demonstrators outside the Turkish ambassador’s residence on Sheridan Circle were indicted.

In the indictment, the Superior Court of the District of Columbia charged the defendants with conspiracy, bias-related hate crimes, assault with a dangerous weapon and assault with significant bodily injury, felonies that are punishable by a statutory maximum of 15 years. Sixteen of the defendants had already been indicted in June. Three security officials, including Kose, were added to the list in Tuesday’s indictment. An initial hearing has been set for Sept. 7.

Coming only weeks before Erdogan is scheduled to address the United Nations General Assembly meeting in New York on Sept. 19, the indictment has prompted worry that the Turkish president may choose to boycott the event just as the administration seeks to repair ties.

In a statement yesterday, the Turkish Foreign Ministry called the indictment “biased” and “purely political” and claimed that the indictment included the names of people who had never even been in the United States.