Law enforcement officials plan to announce charges Thursday against a dozen members of the Turkish president’s security detail for their involvement in a brutal attack on protesters outside the Turkish ambassador’s residence here last month, two American officials said on Wednesday.

The authorities have already charged several others, including two Americans and two Canadians, with taking part in the violent skirmish.

The Washington police have been investigating the May 16 attack along with the State Department and the Secret Service. The police planned to announce the charges at a news conference on Thursday morning, according to the two officials, who spoke on the condition of anonymity to discuss the charges before they were made public.

Washington police officials confirmed that the two Americans are Sinan Narin, of Virginia, and Eyup Yildirim, of New Jersey. Mr. Narin was charged with felony and misdemeanor assault. Mr. Yildirim, who can be seen on video repeatedly kicking a protester, was charged with two felony counts and one misdemeanor assault count. The two did not immediately return calls on Wednesday requesting comment.

The police declined to comment on others facing charges, but were expected to release details on Thursday.

Coming almost a month after the episode, the charges are the most significant retaliatory step taken to date by American authorities, who have fumed privately and publicly over what they see as a highly offensive attack on free speech — not to mention American law enforcement.

Lawmakers from both parties on Capitol Hill, as well as a smattering of advocacy groups, have clamored that those responsible for the assault be prosecuted. Last week, the House unanimously passed a resolution condemning the attack and calling for charges against the security forces.

One of those lawmakers, Representative Edward R. Royce, the chairman of the House Foreign Affairs Committee, welcomed news of the charges, urging the State Department on Wednesday to “double down” on its efforts to “bring these individuals to justice.”

In calibrating its response, though, the Trump administration has had to tread carefully, navigating a web of diplomatic and military concerns with a key NATO ally. The episode appears to have already stalled a proposed $1.2 million small-arms sale to Turkish security forces that was moving toward approval by the State Department last month.

And then there was the added wrinkle that the entire security detail for President Recep Tayyip Erdogan of Turkey had left the country with him just hours after the attack. Members of the security team face several felony and misdemeanor counts, the American officials said.

It is highly unlikely that Turkey would extradite the men to the United States to face the charges, but they do face the possibility of arrest should they ever try to re-enter the country.

The State Department said in a statement on Wednesday that it would weigh additional action against those who have been charged, “as appropriate under relevant laws and regulations.”

“Any further steps will be responsive and proportional to the charges,” the department said.

The Turkish Embassy here did not immediately respond to requests for comment. In a statement in the days after the attack, the embassy said that anti-Erdogan protesters had caused the violence by “aggressively provoking” Turkish-American citizens who had gathered to greet the president and who responded in self-defense. The statement did not mention the security forces.

The run-in was not the first time Mr. Erdogan’s bodyguards have become violent while visiting the United States. In 2011, they took part in a fight at the United Nations that sent at least one security officer to the hospital. And last year, the police and members of Mr. Erdogan’s security team clashed with demonstrators outside the Brookings Institution in Washington.

But the latest case, which played out in broad daylight along Washington’s genteel Embassy Row, has brought a much higher level of attention. Videos that were streamed live from the scene (and later spread across social media) showed armed guards storming a small group of peaceful, anti-Erdogan protesters in plain sight of federal and local law enforcement officers.

A chaotic and bloody scene followed in which the guards, the protesters, pro-Erdogan civilians and American law enforcement tangled on the street and in a nearby park. Nine people were hospitalized, some with serious injuries.

The New York Times, after analyzing videos and photos from the scene, identified at least 24 men, including armed Turkish security forces, who had attacked protesters. Another video shows Mr. Erdogan watching the attack play out from a Mercedes-Benz sedan parked a few yards away. His role in the clash, if any, is unclear.

Diplomatic security officers protecting the delegation also temporarily detained two members of the Turkish forces who had assaulted them, before it was determined that the guards had diplomatic status and were freed.

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