One of the world’s largest news agencies has instructed its journalists to "practice skills learned" in hostile countries and warzones while reporting on the Trump administration.

In a message to thousands of Reuters reporters and photographers, its editor-in-chief offered advice on how to address the many “challenges” raised by Donald Trump’s presidency.

“It’s not every day that a US President calls journalists ‘among the most dishonest human beings on earth’ or that his chief strategist dubs the media ‘the opposition party’,” Steve Adler wrote.

“We don’t know yet how sharp the Trump administration’s attacks will be over time or to what extent those attacks will be accompanied by legal restrictions on our news-gathering.”

Donald Trump attacks 'dishonest' media over CIA speech

Mr Adler said that although there had been debate over whether to oppose Mr Trump’s administration or boycott its press briefings, Reuters would continue the unbiased style of reporting it uses in countries “in which the media is unwelcome and frequently under attack”.

He cited examples as Turkey, the Philippines, Egypt, Iraq, Yemen, Thailand, China, Zimbabwe and Russia, where journalists have been detained, killed, prosecuted, attacked, threatened, censored and denied visas.

“Don’t take too dark a view of the reporting environment: It’s an opportunity for us to practice the skills we’ve learned in much tougher places around the world,” the editor added.

Journalists are being advised to become “ever more resourceful” and “worry less about official access”, and not to be intimidated.

Reuters sources said the email had originally been sent internally to staff but was published in full after being leaked.

It came amid continued concern over Mr Trump’s treatment of the “mainstream” media, seeing him repeatedly target outlets including CNN and the New York Times, which have been critical of his policies.

His repeated use of the phrase “dishonest media” has been compared to the Nazi-era term “Lügenpresse”, meaning lying press, which has been used at right-wing events attended by the Republican’s supporters.

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Mr Trump has spurned traditional methods of communication, delaying and cancelling press briefings following his election, and granted interviews with sympathetic minor outlets like the Christian Broadcasting Network over larger publications and networks.

Last week he accused the press of “distorting” his words to disparage him, saying he used his Twitter account to get his message across instead.

Mr Trump’s tweets have become notorious for his attacks on media outlets, which were repeating in speeches and on the campaign trail, where he was lambasted for appearing to mock a disabled reporter last year.

The new US President’s style has earned unfavourable comparisons to his Turkish counterpart, who has seen dozens of journalists detained and newspapers closed in widespread purges since an attempted coup.

Recep Tayyip Erdogan praised Mr Trump for putting a CNN reporter “in his place” after he refused to take questions from the US broadcaster at a pre-inauguration press conference.

His pick for chief strategist was Steve Bannon, the chairman of self-declared “alt-right” website Breitbart, which is accused of propagating “fake news” with its vehemently anti-immigration agenda.

Meanwhile the new White House spokesman, Sean Spicer, has been ridiculed for holding up printed notes at official briefings and appearing to contradict the President’s own words on his controversial executive order temporarily banning refugees and visitors from seven Muslim-majority countries.