The US House of Representatives canceled its planned Thursday session, after the Capitol Police warned on Wednesday that a militia group could be plotting to breach the building that was subjected to a deadly attack on 6 January.
The House had been scheduled to debate and vote on a police reform bill, but a Democratic aide said plans changed due in part to the police warning, based on intelligence that "an identified militia group" could present a security threat.
The Senate will convene as planned to begin debating president Joe Biden's $1.9 trillion Covid-19-relief bill on Thursday.
Authorities have said right-wing extremists were among a mob of supporters of former president Donald Trump that stormed the Capitol on 6 January, interrupting the formal certification of Biden's election victory.
Some right-wing conspiracy theorists have falsely claimed that Trump, defeated by Biden in the 3 November election, will be sworn in for a second term on Thursday.
The Justice Department has charged more than 300 people with taking part in the January Capitol siege, in which five people, including a police officer were killed. Among those arrested were members of the right-wing groups called the “Oath Keepers”, “Three Percenters” and “Proud Boys”. The Oath Keepers and Three Percenters are armed militia groups.
"The United States Capitol Police Department is aware of and prepared for any potential threats towards members of Congress or towards the Capitol complex," it said in its statement.
It said it is working with local, state and federal agencies "to stop any threats to the Capitol," adding, "We are taking the intelligence seriously." It did not disclose the nature of the intelligence.
The statement noted that police have made "significant security upgrades" at the Capitol, home to the US House of Representatives and Senate.
On Tuesday, acting House sergeant at Arms Timothy Blodgett notified Congress members of a possible security threat spanning Thursday through Saturday. It referred to "potential protests and demonstration activity surrounding what some have described as the 'true Inauguration Day’."
For nearly a century, US presidents have been inaugurated on 20 January, including Biden, who took the oath of office on the grounds of the Capitol. Previously, 4 March had been the swearing-in date.
Acting Capitol police chief Yogananda Pittman testified to Congress on 25 February that Trump supporters who launched the January attack have indicated they want to "blow up" the building and kill the lawmakers.
Since 6 January, National Guard troops have been dispatched to the Capitol grounds and tall fencing has been erected to extend the security perimeter. Blodgett told lawmakers the Capitol Police department has "enhanced" its security posture.
Congress has held hearings on the riot and congressional leaders in coming days are expected to receive recommendations for new, permanent security measures at the Capitol.
The House impeached Trump on 13 January on a charge of inciting an insurrection, focusing on an incendiary speech he made to supporters shortly before the mob converged on the Capitol. The Senate acquitted him on 13 February.