Donald Trump declines to answer questions related to his family business during deposition at New York attorney general's office, saying he has "no choice" but to invoke the constitutional guarantee.

Trump has undergone many depositions, dating to his career as a real estate developer.
Trump has undergone many depositions, dating to his career as a real estate developer. (AP)

Former US president Donald Trump has invoked his Fifth Amendment protection against self-incrimination as he testified under oath in the New York attorney general's long-running civil investigation into his business dealings.

About an hour after arriving at Attorney General Letitia James' Manhattan offices on Wednesday, Trump said he "declined to answer the questions under the rights and privileges afforded to every citizen under the United States Constitution."

"I once asked, 'If you're innocent, why are you taking the Fifth Amendment?' Now I know the answer to that question," the statement said. "When your family, your company, and all the people in your orbit have become the targets of an unfounded politically motivated witch hunt supported by lawyers, prosecutors and the fake news media, you have no choice."

As vociferous as Trump has been in defending himself in written statements and on the rally stage, legal experts said answering questions in a deposition was risky because anything he said could potentially be used against him in a parallel criminal investigation by the Manhattan district attorney. 

The Fifth Amendment protects people from being compelled to become witnesses against themselves in a criminal case.

Also, in case the attorney general's investigation leads to a civil case against Trump and it goes to trial, jurors could be told that he invoked his protection against self-incrimination.

READ MORE: Republicans dub FBI raid on Trump house 'weaponised politicisation'

'Mob takes the Fifth'

Wednesday's events unfolded two days after FBI agents searched Trump's Mar-a-Lago estate in Florida as part of an unrelated federal probe into whether he took classified records when he left the White House.

New York's investigation is led by Attorney General James, a Democrat who has said in court filings that her office has uncovered "significant" evidence that Trump's company misled lenders and tax authorities about the value of prized assets like golf courses and skyscrapers.

The company, Trump Organization, even exaggerated the size of Trump's Manhattan penthouse, saying it was nearly three times its actual size — a difference in the value of about $200 million, James' office said.

Trump has denied the allegations, contending that seeking the best valuations is a common practice in the real estate industry. He has also accused Attorney General James, who is Black, of racism in pursuing the investigation.

Trump previously criticised people for exercising Fifth Amendment rights.

"The mob takes the Fifth," Trump said during a 2016 campaign rally. "If you're innocent, why are you taking the Fifth Amendment?"

He was referring to people who had exercised their Fifth Amendment rights in an investigation relating to Democrat Hillary Clinton's use of a private email server for official correspondence during her time as secretary of state. 

Clinton was Trump's opponent in the presidential election that year.

READ MORE: Explainer: Why is Trump facing a presidential records probe?

Source: TRTWorld and agencies