WASHINGTON — Supporters of President Recep Tayyip Erdogan of Turkey, including his government security forces and several armed individuals, violently charged a group of protesters outside the Turkish ambassador’s residence here on Tuesday night in what the police characterized as “a brutal attack.”
Eleven people were injured, including a police officer, and nine were taken to a hospital, the Metropolitan Police chief, Peter Newsham, said at a news conference on Wednesday. Two Secret Service agents were also assaulted in the melee, according to a federal law enforcement official.
The State Department condemned the attack as an assault on free speech and warned Turkey that the action would not be tolerated. “We are communicating our concern to the Turkish government in the strongest possible terms,” said Heather Nauert, a State Department spokeswoman.
A group of Republican lawmakers went a step further, calling the episode an “affront to the United States” and calling for Turkey to apologize.
Photos and videos posted on social media by witnesses showed a chaotic scene of flying fists, feet and police batons — all in the middle of rush hour traffic along stately Embassy Row. The video showed two men bleeding from the head and men in dark suits punching and kicking protesters, some lying on the ground.
The initial rush devolved into several smaller skirmishes as uniformed police officers, some in helmets and swinging collapsible batons, struggled to restore order. The Anadolu Agency, a state-owned Turkish news service, reported that members of the president’s security team were involved in the attack.
The confrontation came after President Trump welcomed Mr. Erdogan to the White House on Tuesday and praised him as a stalwart ally in the battle against Islamic extremism. Mr. Trump did not speak of Mr. Erdogan’s authoritarian crackdown on his own people.
The White House has thus far been silent on the episode. Sean Spicer, the White House press secretary, referred reporters to the State Department and declined to comment further.
The Turkish embassy released a statement late Wednesday that contradicted United States officials and video evidence and blamed the demonstrators, who, it said, had been “aggressively provoking Turkish-American citizens who had peacefully assembled to greet the president.” The president’s supporters and security forces were reacting in self-defense, the statement said.
The altercation, which played out in broad daylight and ricocheted across social media on Tuesday, puts the United States in an uncomfortable position as it must navigate investigating and potentially charging the security personnel and other Erdogan supporters involved in the attack, who could potentially claim diplomatic immunity.
Chief Newsham demurred when asked whether members of Mr. Erdogan’s security team were involved in the attack, but the State Department later acknowledged their presence. Mr. Erdogan and his security guards have since left the country. It was unclear if embassy staff had also been involved.
Chief Newsham said an investigation was continuing, adding that the authorities were reviewing video from the scene and had a good sense of who was involved. He said that some members of the pro-Erdogan group were carrying firearms, which made it more difficult for the police to contain the scene.
“We intend to assure that there is accountability for anyone involved in this assault,” Chief Newsham said. “Yesterday we witnessed what appeared to be a brutal attack on peaceful protests.”
The Secret Service, which provides protection for visiting dignitaries, said in a statement it would work with the police and the State Department “to aggressively pursue accountability for those involved in yesterday’s protests.”
The violence came after several hours of peaceful protest staged by a coalition of groups who oppose Mr. Erdogan’s policies on a range of issues, from his government’s stance toward the Kurds and Armenians to his perceived assault on the country’s democratic institutions.
The police said two people were arrested Tuesday evening. Ayten Necmi, 49, of Woodside, N.Y., was charged with aggravated assault, and Jalal Kheirabaoi, 42, of Fairfax, Va., was charged with assault on a police officer. Protest organizers said those arrested were part of their group.
The episode was not the first time that Turkish security forces have ignited violence in the American capital. The police and members of Mr. Erdogan’s security team clashed with demonstrators last year outside the Brookings Institution, where Mr. Erdogan was giving a speech. Brookings wrote on its website that his bodyguards had “behaved unacceptably — they roughed up protesters outside the building and tried to drag away ‘undesired’ journalists, an approach typical of the Russians or Chinese.”
Aram Hamparian, the executive director of the Armenian National Committee of America, who posted a video of Tuesday’s clash on his organization’s Facebook page, said that when Mr. Erdogan and his entourage arrived at the ambassador’s residence around 4 p.m., the president’s supporters gathered and rushed across the street and into the park where the protest was taking place.
Several of the protesters said they were caught off-guard when the group rushed through the police and into their ranks, which included some small children. All nine demonstrators who were hospitalized have since been released, but Mr. Hamparian said many left with stitches.
Lucy Usoyan of Arlington, Va. was among them. Ethnically Yazidi and raised in Armenia before moving to the United States, she said she had expected a mostly quiet afternoon expressing her displeasure at Mr. Erdogan’s government.
Instead, she said, she ended up knocked to the ground and kicked until she was briefly unconscious.
“When I opened my eyes I saw people all around,” said Ms. Usoyan, 34. “Some were bleeding, and I could not get up.”
Sayid Reza Yasa, one of the organizers of the demonstration, said he lost at least one tooth and his nose was bloodied as he was knocked to the ground and kicked repeatedly before the police intervened.
Mr. Yasa, 60, an American citizen who was born in Turkey and is of Kurdish descent, said he was familiar with the brutality of Mr. Erdogan’s forces, but surprised by their audacity on Tuesday.
“This is not acceptable,” Mr. Yasa said. “This is America. This is not Turkey.”
Correction: May 17, 2017
An earlier version of this article misstated the location of the confrontation. It was on a grassy area in front of the Turkish ambassador’s residence, the former embassy in Washington, not the current embassy several blocks away.