The US Supreme Court on Monday allowed the release of Donald Trump's tax records to criminal prosecutors, rejecting a last-ditch bid by the former president's lawyers to keep them secret.

Trump, 74, has been waging a protracted legal battle to prevent his tax records from being handed over to New York prosecutors probing hush payments to women and possible fraud.

The nation's highest court denied the request filed by lawyers for Trump without comment, paving the way for the documents to be handed over to Manhattan District Attorney Cyrus Vance.

The prosecutor, a Democrat, has been fighting for over a year to obtain eight years of Trump's tax returns as part of an investigation into the ex-president's finances.

Monday's ruling concerns a subpoena that Vance had issued to Trump's accountants Mazars USA in August 2019 ordering it to furnish documents stretching back to 2011.

"The work continues," Vance said in a three-word statement issued after the ruling.

Vance's probe was initially focused on payments made before the 2016 presidential election to two women who claim they had affairs with Trump, including porn star Stormy Daniels.

Former US president Donald Trump had appealed to the Supreme Court to prevent his tax records from being handed to prosecutors
Former US president Donald Trump had appealed to the Supreme Court to prevent his tax records from being handed to prosecutors AFP / MANDEL NGAN

But the state-level investigation is also now examining possible allegations of tax evasion, and insurance and bank fraud.

Trump, who left the White House last month, called the investigation "a continuation of the greatest political witch hunt in the history of our country."

"The Supreme Court never should have let this 'fishing expedition' happen, but they did," he said in a statement following the ruling.

US presidents are not required by law to release details of their personal finances but every US leader since Richard Nixon has done so.

Trump repeatedly said he would release them pending an audit but ultimately broke with the tradition.

Vance's investigators have interviewed Trump's former personal lawyer Michael Cohen, who received a three-year prison term after admitting making hush payments to the two women.

The ex-lawyer had testified to Congress that Trump and his company artificially inflated and devalued the worth of their assets to both obtain bank loans and reduce their taxes.

Manhattan prosecutor Cyrus Vance, seen here in February 2020, investigating Donald Trump's tax affairs
Manhattan prosecutor Cyrus Vance, seen here in February 2020, investigating Donald Trump's tax affairs GETTY IMAGES NORTH AMERICA / Yana Paskova

If Trump were charged and convicted he could face a possible jail term. Unlike federal offenses, state crimes are not subject to presidential pardons.

Investigators also recently interviewed employees of Deutsche Bank, which has long backed the former president and the Trump Organization, US media reported.

They spoke to staff at Trump's insurance broker Aon, too.

Vance's investigation is taking place behind closed doors in front of a Grand Jury.

It is unclear if and when it will lead to a prosecution, which would be the first of a former US president.

In July, the Supreme Court rejected Trump's argument that as a sitting president he was immune from prosecution.

Trump's lawyers then challenged the scope of the requested documents, saying it was too broad.

Ahead of the November 3 election, The New York Times alleged that Trump had avoided paying federal taxes in 11 out of the 18 years for which it had obtained returns.

The newspaper also reported that Trump paid just $750 in federal income taxes in 2016 and 2017, a claim the former president denies.

New York state's Attorney General Letitia James is also investigating allegations of bank fraud and insurance fraud through civil proceedings.

Trump's legal troubles may not end there.

Senate Republican leader Mitch McConnell has said that as a civilian Trump "is liable for everything he did while he was in office."

At his historic second impeachment trial, the US Senate acquitted Trump of inciting the crowd that stormed the US Capitol in January, but McConnell suggested Trump could face criminal and civil action over the riot.

In February, prosecutors in Georgia opened an investigation "into attempts to influence" the presidential election in the state.

Trump had pressured officials to overturn his loss in the key battleground.