Donald Trump has said he is being “unfairly attacked”, as the former US president’s family business becomes the subject of a criminal investigation.

The Trump Organization has been the focus of a civil probe by the New York attorney general over whether it falsely reported property values to secure loans and obtain economic and tax benefits.

But on Wednesday, the office of Letitia James announced that it was “no longer civil in nature”, adding: “We are now actively investigating the Trump Organization in a criminal capacity, along with the Manhattan DA.”

In response, Mr Trump referred to himself in the third person as he accused Ms James, who is a Democrat, of having “literally campaigned on prosecuting Donald Trump even before she knew anything about me”.

Writing on his blog (he remains banned from Twitter), the Republican said: “She said that if elected, she would use her office to look into ‘every aspect’ of my real estate dealings.

“She swore that she would ‘definitely sue’ me.

“She boasted on video that she would be, and I quote, ‘a real pain in the a**’.”

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He also stated that the investigation is “corrupt” and a “desperate search for a crime”, as he accused the district attorney’s office of “going after me for years”.

“Our movement, which started with the great election win of 2016, is perhaps the biggest and most powerful in the history of our country,” Mr Trump added. “But the Democrats want to cancel the Make America Great Again movement, not by Making America First, but by Making America Last.”

“No President has been treated the way I have,” he continued. “With all of the crime and corruption you read about with others, nothing happens, they only go after Donald Trump.”

Mr Trump had previously branded the inquiry a “witch hunt”.

Ms James is looking into whether The Trump Organization falsely reported real estate values to get loans and receive tax and economic benefits.

This includes inflating the value of assets to secure higher lending and undervaluing properties to get tax breaks.

Among the properties in question are two in New York – his northern Manhattan estate and his eponymous tower.

Others include a hotel in Chicago and a Los Angeles golf course.

Manhattan’s district attorney Mr Vance, also a Democrat, has been investigating Mr Trump’s pre-presidency business dealings for more than two years.

While the exact nature of that probe is not known due to US grand jury rules, Mr Vance’s office has revealed in court filings that it was investigating “possibly extensive and protracted criminal conduct” at The Trump Organization, including tax and insurance fraud and falsification of business records.

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Mr Vance’s investigation started after Mr Trump’s former lawyer Michael Cohen allegedly paid two women to be silent about claimed sexual relationships with Mr Trump in the run-up to the 2016 presidential election.

Mr Vance has sought evidence from the former daughter-in-law of The Trump Organization’s chief financial officer, Allen Weisselberg