The US House of Representatives has cancelled a planned session after Capitol Police warned a militia group could be plotting to breach the building again.
The House had been scheduled to debate and vote on a police reform bill on Thursday (local time).
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 $US1.9 ($A2.4) trillion COVID-19-relief bill on Thursday.
The cancellation came after US Capitol Police officials said on Wednesday (local time) they had “obtained intelligence that shows a possible plot to breach the Capitol by an identified militia group on Thursday, March 4”.
In a statement posted to Twitter, Capitol Police said the intelligence – which an FBI bulletin said could involve the extremist Three Percenters group – was being taken seriously.
“Our department is working with our local, state, and federal partners to stop any threats to the Capitol. We are taking the intelligence seriously,” it said.
“Due to the sensitive nature of this information, we cannot provide additional details at this time.”
Authorities have said right-wing extremists were among a mob of Trump supporters that stormed the Capitol on January 6, interrupting the formal certification of Mr Biden’s election victory.
Some right-wing conspiracy theorists continue to claim that Mr Trump, who lost November’s presidential election to Mr Biden, 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 right-wing groups, including the Three Percenters and the Oath Keepers 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.
The statement noted police had made “significant security upgrades” at the Capitol.
On Tuesday, Acting House Sergeant at Arms Timothy Blodgett notified members of a possible security threat from Thursday until 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 January 20, including Mr Biden, who took the oath of office on the grounds of the Capitol. Before that, March 4 was the swearing-in date.
Acting Capitol Police Chief Yogananda Pittman testified to Congress on February 25 that Trump supporters who launched the January attack have indicated they want to “blow up” the building and kill lawmakers.
The US Capitol complex remains surrounded by temporary fencing topped with razor wire following the January riots. There are also 5000 National Guard troops on site and across Washington.