Man charged over threats to Boston Globe

A California man has been charged with threatening to kill Boston Globe employees in retaliation for the newspaper's role in a defence of press freedoms by hundreds of US news organisations against attacks by President Donald Trump.

In a case unsealed on Thursday, federal prosecutors said Robert Chain, 68, called journalists "the enemy of the people" in threatening phone calls that echoed the phrase Trump has used to criticise unflattering news coverage.

"In a time of increasing political polarisation, and amid the increasing incidence of mass shootings, members of the public must police their own political rhetoric. Or we will," Andrew Lelling, the US attorney for Massachusetts said in a statement on the arrest.

Prosecutors said Chain, a resident of Los Angeles, was arrested on Thursday on a felony count of making threats in interstate communications.

If convicted, he could face up to five years in prison.

Prosecutors said Chain made 14 threatening calls to the Globe from August 10 through August 22, including on August 16 - the day the press freedom editorials ran - when he threatened to shoot employees in the head.

That prompted authorities to station police outside the paper's Boston building.

In Los Angeles on Thursday, a federal magistrate ordered Chain be released on $US50,000 ($A68,860) bond and to appear in federal court in Boston on September 24.

The Globe announced its plan on August 10 for co-ordinated editorials defending press freedoms, which

Newspapers and other media outlets across the United States joined in on August 16.

The editorials led Trump to lash out on Twitter, saying: "THE FAKE NEWS MEDIA IS THE OPPOSITION PARTY. It is very bad for our Great Country....BUT WE ARE WINNING!"

He did not provide specifics.

Trump continued bashing news media organisations on Wednesday and Thursday, lashing out at NBC and CNN, and again using the phrase "enemy of the people".

In June, five people were fatally shot at a newspaper in Annapolis, Maryland, by a man prosecutors allege had a long-standing grudge against the paper.