The New York attorney general’s office has told a court that its investigators have uncovered evidence that Donald Trump’s company used “fraudulent or misleading” asset valuations to get loans and tax benefits.

The court filing late on Tuesday said state authorities had not yet decided whether to bring a civil lawsuit in connection with the allegations, but that investigators needed to question Trump and his two eldest children as part of their inquiries.

The former US president and his lawyers say the investigation is politically motivated.

In the court documents, the office of the attorney general, Letitia James, gave its most detailed accounting yet of its investigation into allegations that Trump’s company repeatedly misstated the value of assets to get favourable loan terms or reduce its tax burden.

Using personal financial statements from 2004 to 2020 that were filed by Trump’s accounting firm, Mazars, the attorney general’s office said the Trump Organization overstated the value of land donations made in New York and California on paperwork submitted to the IRS to justify several million dollars in tax deductions.

The company misreported the size of Trump’s Manhattan penthouse, saying it was nearly three times its actual size – a difference in value of about $200m (£147m), James’s office alleged, citing deposition testimony from Trump’s longtime financial chief Allen Weisselberg, who was charged last year with tax fraud in a parallel criminal investigation.

Valuations of Trump golf clubs in Westchester county, New York and Scotland were inflated, the attorney general’s office says, with the Trump Organization claiming that multiple, ultimately nonexistent mansions worth millions of dollars had been built on the family’s family estate. The company also claimed that there were $150,000 initiation fees into Trump’s Westchester golf course that were never collected.

Citing this new additional evidence that Trump and the Trump Organization made fraudulent and misleading asset valuations to boost their appearance to potential lenders and investors, James’ office detailed its findings in a court motion seeking to force Trump, his daughter Ivanka Trump and his son Donald Trump Jr to comply with subpoenas seeking their testimony.

Messages seeking comment were left with lawyers for the Trumps.

Trump’s legal team has sought to block the subpoenas, calling them “an unprecedented and unconstitutional manoeuvre”. They say James is improperly attempting to obtain testimony that could then be used in the parallel criminal investigation, being overseen by the Manhattan district attorney, Alvin Bragg.

Trump sued James in federal court last month, seeking to put an end to her investigation. In the suit, his lawyers claimed the attorney general, a Democrat, had violated the Republican’s constitutional rights in a “thinly veiled effort to publicly malign Trump and his associates”.

In the past, the Republican ex-president has decried James’s and Bragg’s investigations as part of a “witch-hunt”.

In a statement late on Tuesday, James’s office said it had not decided whether the evidence outlined in the court papers merited legal action, but the investigation should proceed unimpeded.

“For more than two years, the Trump Organization has used delay tactics and litigation in an attempt to thwart a legitimate investigation into its financial dealings,” James said.

“No one in this country can pick and choose if and how the law applies to them. We will not be deterred in our efforts to continue this investigation and ensure that no one is above the law.”

Although James’s civil investigation is separate from the criminal investigation, her office has been involved in both, sending several lawyers to work side by side with prosecutors from the Manhattan DA’s office.

One judge has previously sided with James on other matters relating to the investigation, including making another Trump son, the Trump Organization executive Eric Trump, testify after his lawyers abruptly cancelled a scheduled deposition.

Last year, the Manhattan district attorney brought tax fraud charges against the Trump Organization and Weisselberg. Weisselberg pleaded not guilty to charges alleging he and the company evaded taxes on lucrative fringe benefits paid to executives.

Both investigations are at least partly related to allegations made in news reports and by Trump’s former personal lawyer Michael Cohen that Trump had a history of misrepresenting the value of assets.

Associated Press contributed to this report