Nine people were injured Tuesday afternoon during a demonstration outside the Turkish Embassy on Washington's embassy row.
All nine were taken to hospitals, and at least one was reported to be in serious condition.
From initial accounts, it appeared that fighting may have broken out between opposing groups of demonstrators. Police spokesman Dustin Sternbeck said two people were arrested.
The demonstration comes as Turkish President Recep Tayyip Erdogan met with President Donald Trump in the White House.
Turkey and the United States have disagreed over U.S. plans to arm Kurdish fighters.
The protest on Tuesday took place outside the ambassador's residence. Traffic there was backed up for a time.
It was not clear whether the apparent dispute at the protest involved clashes between Erdogan supporters and those who oppose him over such matters as the Kurdish issue.
There is a Kurdish insurgency in Turkey, which both the United States and Turkey consider a terrorist organization.
Erdogan is staying at Blair House across from the White House during his visit, and was apparently not at the embassy during the demonstration.
Embassy officials could not be reached immediately.
The Secret Service referred questions to the District of Columbia police which patrolled at the demonstration.