D.C. riot police form a line across K Street Northwest at 13th Street as protesters react to the swearing in of President Trump in January. (James Lawler Duggan/Reuters)

The American Civil Liberties Union on Wednesday sued the D.C. police, accusing them of arresting innocent protesters while quelling a violent disturbance during the presidential inauguration and detaining people for up to 16 hours without food, water and bathroom ­facilities.

The suit, which does not specify monetary damages, was filed in federal court and alleges abuse by officers who the civil liberties group say indiscriminately fired pepper spray in ­30-foot plumes and subjected some detainees to body cavity searches after the unrest Jan. 20 in downtown Washington.

Four plaintiffs are named in the suit — an independent journalist, a legal observer and two protesters — but the rights group asserts that many of the 230 arrested were similarly affected. All four deny participating in breaking store and car windows and say they got swept up in what the ACLU describes as a “stampede created” by police in the “pursuit of demonstrators.”

Scott Michelman, a senior attorney for the ACLU of the District of Columbia, said at a news conference that many of the people detained that day had nothing to do with the violence but were arrested out of “guilt by association” with the small group of agitators.

Scott Michelman, a senior attorney for the ACLU of the District of Columbia speaking at a press conference to announce filing of lawsuit against DC police alleging authorities indiscriminately fired pepper spray at demonstrators while trying to quell a disturbance in Franklin Square on Jan. 20, Inauguration Day. (Peter Hermann/TWP)

“It is clear to me that the Metropolitan police came out on Inauguration Day intent on teaching demonstrators a lesson and chilling political speech in the nation’s capital,” Michelman said in an interview. Named in the suit are the District, Police Chief Peter Newsham and up to 170 unidentified officers.

Dustin Sternbeck, the lead spokesman for the police department, said that on Inauguration Day, “there were thousands of individuals who exercised their constitutional right to peacefully assemble and speak out for their cause. Unfortunately there was another group of individuals who chose to engage in criminal acts, destroying property and hurling projectiles, injuring at least six officers.”

Sternbeck said that suspects were arrested and that “the bulk of them are pending prosecution after being indicted by a grand jury.” He also added that “allegations of misconduct will be fully investigated.”

In May, Newsham pushed back against accusations that innocent bystanders were arrested. He described the disturbance as “a small riot in our city” and said, “I hate the fact there are people pushing the false narrative that the MPD indiscriminately arrested people who were here to protest.”

Authorities have said that rioters, including some dressed all in black and armed with hammers and crowbars, caused an estimated $100,000 in damage to vehicles and buildings in a ­16-square-block area around Franklin Square. Prosecutors have said the demonstrators employed means akin to “black bloc” tactics most commonly linked to anarchists. One officer was hit in the head with a chunk of concrete.

Police used pepper spray and, according to the police labor union, “sting grenades” that set off loud noises and bright flashes and that shoot out small rubber pellets that sting.

Those arrested said they were corralled on a street corner and arrested without being given an order to disperse. Police said a dispersal order wasn’t necessary after the demonstration turned violent.

Authorities said that corralling to arrest is an important distinction from the roundup of nearly 400 largely peaceful protesters in Pershing Park in 2002 that led to lawsuits and cost the District upward of $11 million. Police surrounded the Pershing Park demonstrators and ordered them to leave but gave them no way to move out.

But Michelman of the ACLU sees little difference and said, “It seems they haven’t learned their lesson about where the constitutional lines are.” He said police in Franklin Square “did not make an attempt to separate out the people who had engaged in unlawful acts from law-abiding demonstrations. They ended up with a massive detention of people they had chased into their own kettle.”

In total, 234 people were charged by police or through an indictment in connection with the Inauguration Day ­disturbance.

Twelve defendants have pleaded guilty, one man to felony rioting and assaulting an officer. He faces three years in prison on each count at his sentencing, set for July. The others pleaded guilty to misdemeanors and were given suspended jail sentences, fined and ordered to community service. Cases against 20 defendants have been dismissed, leaving a total of 202 facing trial.

Protesters said they were held for seven to 16 hours at K and 12th streets as police processed arrests and bused them to a police training center at Blue Plains. There, they were held in a cavernous building built with a mock streetscape that is used to teach recruits. Two said in interviews that they were each fed one cheese sandwich, Hawaiian Punch and water.

One of the men suing, Shay Horse, 23, said he was on the street with a camera taking pictures as a freelance journalist and wearing a hooded sweatshirt. He said he was arrested but never got a chance to talk to an officer until he got to the training center. “By then, it was clear no one was getting out,” he said.

Horse said he and others were ushered five at a time into a separate room, where he said an officer searched him and the others. Horse is from New York and has described himself on Twitter as a “scrumptious/rambunctious anarchist.” At the protest, he said, “I was trying to find a good vantage point for my pictures.” Prosecutors have dropped all criminal charges against him.

Also suing is Judah Ariel, a 36-year-old international trade attorney who volunteered for the National Lawyer’s Guild as a legal observer. He said police used pepper spray on him as he watched officers corral the demonstrators. He said he was wearing a neon-green hat commonly used by legal observers, and he described the onlookers as calm.

Two others named in the suit are Elizabeth Lagesse, a Maryland resident who was protesting President Trump; and Milo Gonzalez, who describes himself both as a protester and an aide to journalists.

Criminal cases against Gonzalez and Lagesse are pending.

Ann E. Marimow contributed to this report.