Nine people were hurt and two arrests were made during an altercation at the Turkish ambassador's residence in the US capital during a visit by Turkey's president, Recep Tayyip Erdoğan.
According to witnesses, a brawl erupted when Erdoğan's security detail attacked protesters carrying the flag of the Kurdish PYD party outside the residence. A local NBC television affiliate reported Erdoğan was inside the building at the time.
Metropolitan Police Department spokesman Dustin Sternbeck said the altercation broke out between two groups but he didn't elaborate on the circumstances. He said two people were arrested, including one who was charged with assaulting a police officer.
"All of the sudden they just ran towards us," Yazidi Kurd demonstrator Lucy Usoyan told ABC, adding that she was attacked by a pro-Erdoğan supporter.
"Someone was beating me in the head nonstop, and I thought, 'Okay, I'm on the ground already, what is the purpose to beat me?'"
The altercation came the same day that Erdoğan met Donald Trump at the White House. The State Department declined to comment.
Earlier Trump and Erdoğan had stood side by side at the White House and promised to strengthen strained ties despite the Turkish leader's stern warning about Washington's arming of a Kurdish militia.
Fresh from securing his grip on Turkey with a referendum to enhance his powers, Erdoğan came to the Oval Office with complaints about US support for Kurdish fighters and what Ankara says is Washington's harbouring of the mastermind of a failed coup.
But both leaders also tried to put a brave face on their differences and to renew a key alliance between Nato's leading power and its biggest Muslim member, partners in the fight against the Islamic State group in Syria and Iraq.
"It is absolutely unacceptable to take the YPG-PYD into consideration as partners in the region, and it's going against a global agreement we reached," Erdoğan said, referring to the Kurdish Peoples' Protection Units (YPG) in Syria.
"In the same way, we should never allow those groups who want to change the ethnic or religious structures in the region to use terrorism as a pretext," he added, suggesting that the Kurds were using the anti-Isis fight as cover for separatist nationalism.