A separate video shows Erdogan arriving and sitting in his vehicle as the fight breaks out, before then emerging and watching. Shouting is heard, and Erdogan's security staff was seen storming the protesters. It is unclear if they worked for the embassy or were members of the counter-protest.
Washington police called the violence a "brutal attack on peaceful protesters".
Washington Police Chief Peter Newsham said 11 people and one police officer were injured. Video shows people pushing past police to confront a small group of protesters across the street in Sheridan Circle. A video showed two men bleeding from the head, and men in dark suits punching and kicking protesters, some lying on the ground.
Two men were also arrested by D.C.'s Metropolitan Police Department on the scene - Jalal Kheirabaoi of Fairfax, VA, and Ayten Necmi of Woodside, NY, according to police reports. "Somebody told them to go and beat up on these peaceful demonstrators and I think it should have repercussions, including identifying these people and bringing charges against them".
"Someone was beating me in the head nonstop, and I thought, 'Ok, I'm on the ground already, what is the objective to beat me?'" "And I thought, 'okay I'm on the ground already, what is the objective to beat me?'" They "began aggressively provoking Turkish-American citizens who had peacefully assembled to greet the President".
But Erdogan said he believed Washington "will knock our door on the issue of Syria". "We just celebrated our President".
Ceres Borazan, a Kurd from Turkey, traveled from New Jersey to protest the president's trip.More news: Rampant Madrid on cusp of ending title drought
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The unseemly incident is adding to U.S.
"The fact that the US, which has not taken any steps forward on Gulen despite the insistent demands of Turkey, put Pastor Brunson on the agenda at high-level meetings begs the question: why is the priest important for the USA?" the newspaper asked, implying America was colluding to defend Gulenists.
U.S. expresses concern in "strongest possible terms" after violence erupted outside the Turkish embassy.
State Department spokeswoman Heather Nauert said McGurk has "the full support and backing" of Trump and Secretary of State Rex Tillerson.
Republican Senators Marco Rubio (Florida) and Ted Cruz (Texas) called on the Turkish government to immediately apologize for the violence.
Turkish Foreign Minister Mevlut Cavusoglu said the United States should replace its special envoy to the anti-ISIS coalition, Brett McGurk, because of his perceived support for Kurdish "militants" in northern Syria, Turkey's state news agency Anadolu reported Thursday.
"We should throw their ambassador the hell out of the United States of America", said McCain on MSNBC's "Morning Joe". The embassy alleged, without evidence, that the demonstrators were associated with the Kurdistan Workers' Party, or PKK, which has waged a three-decade-long insurgency against Turkey and is considered a terrorist group by the United States. "Turkey is not a country that will consent to such treatment", Erdogan said.