WASHINGTON • The United States Department of Homeland Security (DHS) has declared a nationwide terrorism alert, citing the potential threat from domestic anti-government extremists opposed to Democrat Joe Biden as president.

Extremists emboldened by the deadly Jan 6 assault on Congress by angry supporters of former president Donald Trump could undertake attacks against elected officials and government facilities, the alert said.

It was the first alert ever issued for domestic violent extremists.

The warning came as the authorities in California charged a Trump supporter and follower of a far-right militia group with possession of five homemade pipe bombs, alleging that he intended to attack Democrats.

The National Terrorism Advisory System Bulletin said the threat of attacks could persist for weeks, in the wake of Mr Biden's Jan 20 inauguration and the storming of the US Capitol.

The DHS said: "Information suggests that some ideologically motivated violent extremists with objections to the exercise of governmental authority and the presidential transition, as well as other perceived grievances fuelled by false narratives, could continue to mobilise to incite or commit violence."

Some security worries surround the impeachment trial of Mr Trump, beginning in the second week of next month.

He has been charged by the House of Representatives with "incitement of insurrection" for allegedly encouraging the assault on the Capitol.

The alert came two days after the Pentagon said thousands of National Guard troops deployed in Washington for Mr Biden's inauguration would remain in the capital until March.

AGENCE FRANCE-PRESSE