Donald Trump has issued his most inflammatory condemnation yet of the impeachment investigation against him, labelling it “a COUP” designed to strip Americans of their freedoms.

The president is being investigated over a phone call to Ukraine‘s Volodymyr Zelensky in which it is said he appeared to attempt to leverage military aid for personal political gain.

On Tuesday night, Mr Trump falsely likened the impeachment process to a coup, typically defined as an illegal and often violent seizure of power from a government.

“As I learn more and more each day, I am coming to the conclusion that what is taking place is not an impeachment, it is a COUP, intended to take away the Power of the People, their VOTE, their Freedoms, their Second Amendment, Religion, Military, Border Wall, and their God-given rights as a Citizen of The United States of America!”

The outburst came as officials inside his administration agreed to provide testimony for the investigation.

Marie Yovanovitch, the former US ambassador to Ukraine, and Kurt Volker, the former special envoy to that country, are expected to appear before the intelligence committee of the House of Representatives later this month.

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He is running on a similar platform of democratic socialist reform Getty The Democrat challengers to Trump in 2020 Joe Biden The former vice president recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well and has since maintained a front runner status in national polling EPA The Democrat challengers to Trump in 2020 Elizabeth Warren The Massachusetts senator is a progressive Democrat, and a major supporter of regulating Wall Street Reuters The Democrat challengers to Trump in 2020 Amy Klobuchar Klobuchar is a Minnesota senator who earned praise for her contribution to the Brett Kavanaugh hearings Getty The Democrat challengers to Trump in 2020 Michael Bloomberg Michael Bloomberg, a late addition to the 2020 race, announced his candidacy after months of speculation in November. He has launched a massive ad-buying campaign and issued an apology for the controversial "stop and frisk" programme that adversely impacted minority communities in New York City when he was mayor Getty Images The Democrat challengers to Trump in 2020 Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but has faced tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Pete Buttigieg The centrist Indiana mayor and war veteran would be the first openly LGBT+ president in American history Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Deval Patrick The former Massachusetts governor launched a late 2020 candidacy and received very little reception. 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The decision by the two diplomats, one of whom is still employed by the state department, will be seen as of considerable significance. Secretary of state Mike Pompeo had said he did not want five of his officials whose testimony had been sought by Democrats to cooperate.

Mr Trump has repeatedly denounced the investigation that has been launched into his actions as a “witch hunt”. At the weekend he sparked controversy when he retweeted the words of a pastor who had warned that if Mr Trump were impeached, it would fracture society in a way similar to the civil war.

Yet the language he used on Tuesday appeared to represent an escalationin his rhetoric, and may have been intended to energise those supporters who believe the president is being undermined from within by the so-called “deep state”.

Indeed, his words echoed those of former Republican House speaker Newt Gingrich, a firm supporter of Mr Trump who claimed in a Fox News opinion article that the real estate mogul was the target of an attempted “coup d’etat” by Democrats.

“So, Pelosi rushes out ... announces, ‘We’re moving forward on impeachment’. They have not yet met with the whistleblower. They have not yet received the transcript of the phone call. Nothing had changed except the sheer pressure of her left. And she couldn’t get away from it!”

He added: “And that sort of captures this whole process. That’s where we are right now. This is not an impeachment; this is a coup d’etat,”

Over the weekend, senior White House advisor Stephen Miller appeared on Fox News to denounce the whistleblower and allege that accusations were not only false, but that the individual was not genuine.