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Turkish security officials were involved in Tuesday’s assault of protesters against President Recep Tayyip Erdogan outside the Turkish ambassador’s residence in Washington, two law enforcement sources tell CNN.

The US State Department said it is “concerned by the violent incidents involving protestors and Turkish security personnel” in a statement on Wednesday.

“Violence is never an appropriate response to free speech, and we support the rights of people everywhere to free expression and peaceful protest,” the statement said. “We are communicating our concern to the Turkish government in the strongest possible terms.”

A State Department official said the Turkish security that was involved appears to be a mix of Turkish embassy and Erdogan security staff.