The FBI says there are plans for armed protests in all 50 state capitals and Washington in the lead-up to president-elect Joe Biden's inauguration, stoking fears of more bloodshed after last week's deadly siege at the US Capitol.
An internal FBI bulletin, first reported by ABC News, said nationwide protests might start this week and extend through Mr Biden's January 20 inauguration, law-enforcement officials said.
Investigators believe some of the protesters will be members of extremist groups, the officials said.
They said the armed protests were planned at all state capitols from January 16 to at least January 20, and at the US Capitol from January 17 to 20.
The FBI issued at least one bulletin before the riots last week, which went out to law-enforcement agencies nationwide.
The memo, sent on December 29, said armed demonstrators could target legislatures, the officials said.
Gen Daniel Hokanson, chief of the National Guard Bureau, on Monday said the Guard was keeping an eye out across the US.
“We’re taking a look across the entire country to make sure that we’re monitoring, and that our Guards in every state are in close co-ordination with their local law-enforcement agencies to provide any support requested,” Gen Hokanson said.
The riots followed weeks of online calls for violence in Washington in the waning days of Donald Trump’s presidency.
A tweet in which Mr Trump promised that last Wednesday’s event would be “wild” fuelled a “month-long frenzy of incitements, strategising and embrace of violence against lawmakers", said a group that tracks online extremist activity.
The Site Intelligence Group on Saturday said the Capitol attack emboldened Trump-supporting extremists.
“No matter how all this plays out, it's only the beginning,” a user wrote on The Donald message board.