WASHINGTON (BLOOMBERG) - Federal prisons in the United States were put on lockdown to prevent violence and permit some personnel to deploy to Washington.

At the same time, Maryland has added to the restrictions on transportation into and out of the capital heading into the Jan 20 inauguration by announcing it would suspend commuter rail service on Sunday (Jan 17). Trains will start to run again on Thursday.

The Federal Bureau of Prisons says it has put its institutions on lockdown "in the light of current events occurring around the country".

"The hope is that this prudent measure is for a short period," said the agency, which looks after more than 150,000 inmates.

It said there was no specific warning or prison incident that triggered the decision, which it described as precautionary.

Some of the bureau's personnel, including special operations units trained to respond to riots, have been deployed to Washington and deputised by the US Marshal's Service in the wake of last week's assault on the US Capitol.

"In coordination with the Department of Justice, the Bureau of Prisons made plans to send specially trained officers to Washington DC this week to assist the department if and as determined to be needed," Mr Justin Long, a spokesman for the bureau of prisons, said in a statement.

Followers of the QAnon conspiracy theory and other far-right supporters of President Donald Trump have been speculating on social media about the large troop presence in Washington ahead of next week's inauguration.

Some, who do not believe Mr Trump lost the election, are saying it's a coup in the making by Mr Biden; others suggest that it is part of Mr Trump's master plan.

Posts on networks such as Telegram and Gab used images of the national guardsmen to argue that "something is happening" in the nation's capital.

Some users on these networks allege without substantiation that the troop build-up is part of a plan by Mr Trump to interrupt Mr Biden's inauguration at the last minute, while others are using it to further discredit the President-elect's victory.

"Those 25,000 armed troops in DC are definitely not temporary," far-right activist and former congressional candidate Laura Loomer wrote on Telegram.

The Maryland Department of Transportation is suspending its Marc commuter train service ahead of Mr Biden's inauguration amid threats of unrest.

To ramp up security efforts, Washington's MetroRail and MetroBus have adjusted their hours and closed several downtown subway stations. Many roads in downtown Washington have also been closed, from K Street NW to the National Mall, and spanning as far as the US Capitol in some areas.

Four bridges connecting Virginia to Washington will be closed to traffic through Thursday.