WASHINGTON (REUTERS) - City officials in Washington on Monday (Jan 4) warned supporters of President Donald Trump not to bring guns to protests this week against congressional certification of his election defeat and enlisted hundreds of National Guard troops to help keep order.

"We have received some information that there are individuals intent on bringing firearms into our city and that just will not be tolerated," Metropolitan Police Chief Robert Contee told a City Hall news conference, adding that anyone found doing so or provoking violence would be arrested.

More than 300 troops will be on hand to support the city government, providing crowd control and aiding fire and rescue services, the DC National Guard said in a statement on Monday.

They will be joined by the US Capitol Police, US Park Police and US Secret Service, Contee said.

The District has some of the United States' strictest gun laws, and forbids open carry of weapons or possession of a handgun without a local license.

Thousands of Trump supporters, including some far-right nationalist groups that openly carry arms at protests elsewhere, are expected to converge on the US capital starting on Tuesday to oppose Congress' certification the next day of the Republican President's Nov 3 election loss to Democrat Joe Biden.

Contee said the protests could be bigger than November and December rallies marred by stabbings and brawls as hundreds of Proud Boys, a group of self-described "Western chauvinists," and other Trump loyalists clashed with counter-protesters, and sought fights with antifa, or anti-fascists, and Black Lives Matter activists.

On Monday, Metropolitan police arrested Proud Boys leader Henry "Enrique" Tarrio, and charged him with destruction of property related to an earlier protest. Tarrio was "in possession of two high capacity firearm magazines" at the time of arrest, a police statement said, and charged with that possession offence as well.

Trump to speak

Trump summoned supporters to this week's gatherings, saying on Twitter on Sunday that "I will be there," and on Friday that "it will be wild." Several rallies are planned for Wednesday, including one outside the US Congress.

The White House has not provided any official schedule, but one person briefed on his plans said Trump will speak to supporters Jan 6 at the Ellipse, a park just south of the White House.

Trump falsely claims that Biden won the election through massive vote-rigging, even though dozens of state and federal court rulings, state election officials of both parties, and the US Justice Department have found no major fraud.

Congress is constitutionally mandated to certify the presidential election results on Wednesday, in what would normally be a formality overseen by Vice-President Mike Pence.

But at least 12 Republican senators and some 140 Republican House of Representatives members pledged to vote against certification of Biden's win, citing Trump's election fraud allegations.

Their move will not change the outcome, DC Mayor Muriel Bowser, a Democrat, told the news conference. "Our Constitution will endure. Joe Biden and Kamala Harris will be the President and the Vice-President of the United States" when they are inaugurated on Jan 20.

Bowser urged residents to stay out of the city centre, where boards hung during racial justice rallies last summer still cover office, restaurant and hotel windows.

Before his arrest, Proud Boys' Tarrio said on social media that "record numbers" of members would attend, suggesting that they may dress in all black like antifa activists. "We will be incognito and we will spread across downtown DC in smaller teams," he said.

The Hotel Harrington and the attached Harry's Bar, popular Proud Boys gathering spots during previous protests, will close on Tuesday and Wednesday.

"While we cannot control what happens outside of the hotel, we are taking additional steps to protect the safety of our visitors, guests and employees," the hotel said on its website.

Meanwhile, newly-elected Representative Lauren Boebert, who has vowed to carry her Glock pistol when she is at work in the US Capitol, has so far failed to fulfil that promise and earned a rebuke on Monday from the DC police chief.

The Republican congresswoman, 34, will be "subjected to the same penalties as anyone else caught on a District of Columbia street carrying a firearm unlawfully," Contee told a news conference on security measures this week as the city girds for a string of protests by supporters of outgoing President Donald Trump.

Boebert had travelled the 2,900km from her home in Rifle, Colorado, to Washington and boasted on Sunday, her first day as a newly sworn-in member of the highly secured US Congress: "I will carry my firearms in DC and in Congress."

The self-described "5-foot tall, 100-pound" member of the House of Representatives backed up that pledge, saying she intends to protect her Second Amendment right to bear arms and that of her constituents - even if things in the nation's capital are not done quite the same way as in Rifle, where she operates the Shooters Grill restaurant.

But Boebert has quickly found that promises are sometimes difficult to keep in Washington.

Two days into the new, 117th Congress, Boebert has reported to work minus the Glock, according to an aide who asked not to be identified.

Never mind that Boebert, who has also made supportive statements about the online conspiracy theory known as "QAnon,"posted a video on Twitter in which she reaches for her Glock semi-automatic pistol, placing it in a holster on her hip. The video then cuts to her striding down a street that appears to be in the city of Washington and then across the US Capitol grounds.

"I don't go to work in a motorcade or armoured car," Boebert said, describing Washington as one of the most dangerous cities in the nation. "I am my best security." That may be so. But the District of Columbia for years has had tough handgun controls and open carry is illegal. Similarly, firearms are generally prohibited on the grounds of the Capitol.

Members of Congress are allowed to have guns, however, in their congressional offices, according to a House source. That policy was mainly intended to let lawmakers display ceremonial weapons on their walls, the source added.

Boebert's aide said she and a posse of other House members would soon propose changing the Democratic-controlled chamber's rules so that she can pack her Glock wherever and whenever she wants.

US Capitol Police, which enforces the law and congressional rules across the Capitol grounds, did not immediately respond to a request for comment.