A New York judge has ordered former US President Donald Trump to testify under oath as part of a financial investigation into his real estate empire.

Judge Arthur Engoron ruled on Thursday that Trump, his daughter Ivanka and his son Donald Junior must comply with subpoenas from New York Attorney General Letitia James.

James says he has collected evidence of fraudulent financial practices by Trump and his Trump Organization.

The Attorney General launched a civil investigation into the Trump Organization in 2019 for possible financial crimes.

She investigates the suspicion that the family holding company artificially inflated the value of real estate when it wanted to obtain loans from banks, and in other cases underestimated it in order to save on taxes or insurance premiums.

Trump denies allegations

James wants to question the ex-president, his eldest son Donald Junior and his daughter Ivanka as part of their investigation and has issued subpoenas.

The Trumps sued against the subpoenas – and were now defeated in court.

You can, however, appeal the decision.

Trump has repeatedly denied the Attorney General's allegations and accused her of conducting politically motivated investigations against him.

James is a member of President Joe Biden's Democratic Party.

Internal investigations and “external sources”

In parallel with the Attorney General's investigation, the Manhattan Attorney's Office is conducting a criminal investigation into Trump Corporation's business conduct.

In July last year, charges were brought against the Trump Organization and its longtime chief financial officer, Allen Weisselberg, for tax fraud.

It was only announced on Monday that Trump's long-standing auditors had parted ways with the former US President as a customer.

Accounting firm Mazars said the Trump Organization's financial statements for nearly a decade "should no longer be relied upon."

Both internal investigations and "external sources" led to this conclusion.