The U.S. Capitol Police said Wednesday that they have information regarding a possible plot by a militant group to breach the Capitol on Thursday, a date that some followers of the QAnon extremist ideology falsely claim will mark former president Donald Trump’s return to the White House.

The department declined to name the group or provide additional details, citing the “sensitive nature” of the information. In a statement, the department said it is “prepared for any potential threats.”

In response, the House canceled a scheduled Thursday session, instead wrapping up planned votes late Wednesday. The Senate, considering President Biden’s $1.9 trillion pandemic relief bill, planned to remain in session Thursday. Members and staff were encouraged to take precautions such as parking in underground garages.

“We have already made significant security upgrades to include establishing a physical structure and increasing manpower to ensure the protection of Congress, the public and our police officers,” police said in the statement.

The Capitol Police and the FBI have been criticized for not acting on intelligence supplied by the FBI’s Norfolk field office shortly before the Jan. 6 attack on the Capitol. Rioters easily swarmed through bicycle rack barricades; Capitol and D.C. police officers were overwhelmed by the pure number of attackers; and the National Guard did not respond to the scene until hours after the siege had begun.

Melissa Smislova, the acting undersecretary of the Office of Intelligence and Analysis in the Department of Homeland Security, said Wednesday that her agency, in coordination with the FBI, issued a bulletin very late Tuesday or very early Wednesday about “extremists discussing March 4th and March 6th.”

March 4, the original Inauguration Day before the passage of the 20th Amendment in 1932, is the date that some on the far right have come to believe — wrongly — that Trump will again rise to power. An FBI official told The Washington Post last week that leaders were aware of the QAnon chatter surrounding March 4, but said, “We don’t have any indication of violence or a specific, credible plot at this time.”

The Homeland Security and FBI bulletin sent late Tuesday warns broadly that “militia violent extremists” pose a threat throughout 2021 and that domestic violent extremists generally have probably been “emboldened” by the events of Jan. 6, according to a person familiar with its contents.

The bulletin — a copy of which was posted online by a Politico reporter and confirmed by The Post — talks of the QAnon “conspiracy theory” surrounding March 4 and adds that, as of late February, an “unidentified group” of militia violent extremists had “discussed plans to take control of the U.S. Capitol and remove Democratic lawmakers” on that date.

The FBI said in a statement Wednesday: “While our standard practice is to not comment on specific intelligence products, the FBI is constantly gathering and sharing intelligence with our law enforcement partners. We are always on alert for any potential threats.”

D.C. police declined to discuss in detail the department’s response to the potential threat, though acting chief Robert J. Contee III said in a statement that Civil Disturbance Units “will have an increased presence around the city to ensure the public’s safety.” A D.C. police spokeswoman said the department was working with other agencies to assess information.

On March 3, commanding general of the D.C. National Guard Maj. Gen. William J. Walker discussed how his request to mobilize against the Capitol mob was delayed. (Blair Guild/The Washington Post)

Chris Rodriguez, director of D.C.’s Homeland Security and Emergency Management Agency, told the D.C. Council on Wednesday afternoon that Mayor Muriel E. Bowser (D), Contee and fire chief John Donnelly had been discussing what to expect.

“At this time, we’re aware of this threat,” Rodriguez said. “Given some of the security measures in the city and the awareness at all levels of government — state, local and federal — we will stay enhanced, continue to watch and make sure the 4th goes off peacefully,” he said.

He added: “We have not seen the types of chatter we saw prior to the 6th [of January], particularly online — the groups do not appear to be mobilizing, and so we do not expect large numbers in the District over the next couple of days.”

Researchers tracking online conversations about March 4 say they have detected far less intense and fewer specific plans for mayhem than before the Jan. 6 siege of the Capitol.

“While we have seen a certain of amount of chatter, we have not seen on any of the platforms any of the incitement and calls to violence we saw before,” said Marc Ginsberg, president of the Coalition for a Safer Web, a nonpartisan group that advocates for technologies and policies to remove extremist content from social media.

Researchers hold out the possibility that individual attacks or acts of violence could be planned on closed, encrypted channels that are far more difficult to monitor than the open platforms, such as Parler and TheDonald.win, that hosted much of the planning ahead of Jan. 6.

After concluding the Senate’s Wednesday business and scheduling the Thursday session to begin at noon, Senate Majority Whip Richard J. Durbin (D-Ill.) acknowledged the “apparent contradiction” in how the two chambers were approaching the rest of this week.

Now chairman of the Judiciary Committee, Durbin said that he would expect to have been briefed by the FBI or Justice Department officials if they considered the threat that serious — and he has not yet been so briefed.

“I don’t know if it’s a tease. You know, we were told the January 6th crowd was coming back for January 20th and they didn’t appear. I can’t tell. But in light of what we went through on January 6th, it’s understandable people are concerned,” Durbin said.

The warning about another potential threat to Congress comes as a date for Biden’s first address on Capitol Hill has not yet been set. New presidents typically deliver a speech to a joint session of Congress in February.

In January, Bowser requested that 500 members of the D.C. National Guard remain activated through March 12, amid concerns about potential extremist activity tied to three events: Trump’s now-concluded impeachment trial, Biden’s address and March 4.

In addition to the National Guard and increased police presence, the Capitol grounds have been surrounded by security fencing since the Jan. 6 insurrection.

Last week, acting Capitol Police chief Yogananda D. Pittman warned lawmakers that members of extremist groups involved in the Jan. 6 riot “want to blow up the Capitol and kill as many members as possible” during Biden’s address.

But after that briefing, members of Congress reacted negatively to the idea of maintaining expansive physical barriers to the Capitol. Both Sens. Tim Kaine (D-Va.) and Chris Van Hollen (D-Md.) said the Jan. 6 riot was largely a failure of intelligence, rather than infrastructure.

“The idea of just making a permanent fortress or a permanent fence is too much of a knee-jerk solution,” Van Hollen said.

Del. Eleanor Holmes Norton (D-D.C.), who has been pushing for removal of the fencing around the Capitol, said Wednesday that in light of the new information, the barriers and increased police presence “may have to be there right now. I think they have to respond to the intelligence.” But she said that she was encouraged to see that some fencing had been reduced earlier in the week and that she will continue to advocate to “return the people’s house to the people.”

On Wednesday, Pittman appeared before Congress to ask for a 21 percent increase to the force’s budget to pay for improved security, with an emphasis on better support and training for officers, and protections for lawmakers.

Pittman said that in the first two months of 2021, officials noted a 93 percent increase in threats against lawmakers compared with the same period of 2020. She proposed a security plan for members that includes a focus on security outside of Washington, D.C. She also said that the Capitol Police plan to establish “a dedicated stand-ready force of two platoons (80 officers) at all times,” to reduce the force’s reliance on partner agencies to respond to emergencies.

Greg Jaffe, Mike DeBonis, Colby Itkowitz, Felicia Sonmez, Karoun Demirjian and Paul Kane contributed to this report.