Prosecutors in Brooklyn say Thomas Welnicki "knowingly and willfully threatened to kill, kidnap, and inflict bodily harm upon" the former US president.

Harris, then the vice-president elect and senator from California, evacuated the Democratic National Committee (DNC) headquarters on Capitol Hill after law enforcement officers discovered the device, said the official, speaking on condition of anonymity.

Biden and his top aides have been reluctant to talk directly about Trump since he took office last January, even as the Republican former president continued to spread lies about his election loss.

The number of hospitalized COVID-19 patients has risen nearly 50 percent in the last week and now exceeds 100,000, according to data collected by Reuters, marking the first time that threshold has been reached in a year.

The White House said Biden would push back against Trump's false claims, adopted by many of his followers, that his election defeat was the result of widespread fraud, as well as attempts to downplay the violence of the worst assault on the Capitol since the War of 1812.

State Attorney General Letitia James, a Democrat, issued the subpoenas seeking their testimony in her years-long civil probe last month, according to the document.

The January 6 attack on the seat of Congress, led by supporters of Donald Trump, was "a harbinger of increasing political violence," and American democracy "is threatened," according to two-thirds of those surveyed for a CBS News poll.

The lawmaker from Georgia is a loud and fervent supporter of Donald Trump and his false claims that the 2020 election was stolen, and is also known for making outlandish anti-vaccine claims and other false statements about the coronavirus pandemic.

"I don't consider him the president of the United States," the retired US Air Force veteran told AFP at his New Hampshire home surrounded by oak and birch trees and houses displaying "TRUMP" signs.

News of Austin's positive test comes after the Pentagon last week tightened restrictions at its headquarters over concern about the highly transmissible Omicron variant that has led to a sharp increase in COVID-19 infections throughout the world.

Was it a simple protest-turned-riot? An insurrection? A coup attempt plotted by Trump? 

The United States had 2,604 cancelled flights, more than half of the 4,529 cancelled worldwide, shortly after 4:30 pm (2130 GMT), according to tracking website FlightAware. 

In a 50-minute call, their second conversation this month, Biden said he needed to see Russia decrease its military build-up near Ukraine, while Putin said sanctions threatened by Washington and allies could lead to a rupture in ties. The call was requested by Putin.

"I would imagine given the size of our country, and the diversity of vaccination versus not vaccination, that it's likely to be more than a couple of weeks, probably by the end of January," he said on CNBC.

Monday's travel woes marked a fourth day of flight cancellations, capping a glum Christmas weekend for thousands of passengers who were left waiting in airport queues and on customer service phone lines to re-book flights.

For the results of the gubernatorial races -- victory in leftward-trending Virginia and an unexpectedly narrow defeat in deeply Democratic New Jersey -- proved one thing beyond doubt: Republicans can win without Donald Trump.

It is estimated that airline carriers globally scrapped at least 2,366 flights on Friday, which fell on Christmas Eve and is typically a heavy day for air travel. Nearly 9,000 more flights were delayed.

"That would increase the prospect of running," Biden told ABC News on Wednesday.

An antigen test that Harris received Wednesday morning as part of regular testing and a PCR test after being notified of the staffer's case both came back negative, the White House said, quoted by Reuters.

In a televised address, Biden formally announced a raft of new measures to combat the winter surge -- including shipping half a billion at home tests -- but denied his administration had failed to adequately prepare for the fresh wave of cases.

The announcement came as the United States is seeing another surge in coronavirus cases, with Omicron accounting for about two-thirds of new infections last week, according to the latest data from the Centers for Disease Control and Prevention.

"The rapid spread of the Omicron variant reinforces that we must all continue to accelerate our efforts to end this pandemic and that none of us are safe until all of us are safe," Blinken said in a statement.

A PCR test Biden received on Monday after being notified of the case came back negative, as did an antigen test he received on Sunday as part of his regular testing, White House spokesperson Jen Psaki said in a statement.

The spike, which was tallied by the Centers for Disease Control and Prevention, is based on data for the week ending on Saturday. During the prior week period, Omicron accounted for only 12.6 percent of US cases.

Boric, 35, garnered nearly 56 percent of the vote compared to 44 percent for ultra-conservative Jose Antonio Kast, who conceded even before the final result was known.

The former student activist only just met the required minimum age to run in the presidential race, seven years after being elected to his first political job as a member of Chile's Chamber of Deputies.

The US Senate unanimously voted to make the US the first country to ban virtually all imports from China's Xinjiang region over forced labor concerns.

One day after the blast in Haiti's second largest city of Cap-Haitien, 75 people were confirmed dead in the latest disaster to hit the poverty-wracked Caribbean nation, riven by gang violence and political paralysis.

Indonesia's top diplomat insists that members of the Group of Seven still need to tackle the root issues causing a widening COVID-19 vaccination gap.

A plan to upgrade Russian-Indonesian ties would put Moscow on par with the United States, which signed its own strategic partnership with Indonesia in 2015.