NEW YORK - Former US President Donald Trump said he has been indicted on charges of mishandling classified documents after he left the White House.

This is a remarkable development that makes him the first former president in U.S. history to face criminal charges by the federal government that he once oversaw.

Mr Trump faces seven charges including unauthorised retention of classified files, US media reported.

Mr Trump said he is due in court in Miami on Tuesday afternoon - making him the first former US president to face federal criminal charges.

The Justice Department did not immediately publicly confirm the indictment, which has not been made public.

As he revealed the charges in a post on Truth Social, Mr Trump - who is campaigning to make a return to the White House in 2024 and is the frontrunner for the Republican nomination- said he was innocent.

“I never thought it possible that such a thing could happen to a former President of the United States, who received far more votes than any sitting President in the History of our Country, and is currently leading, by far, all Candidates, both Democrat and Republican, in Polls of the 2024 Presidential Election. I AM AN INNOCENT MAN!”

In a further post, he added: “This is indeed a DARK DAY for the United States of America. We are a country in serious and rapid decline, but together we will Make America Great Again!”

Mr Trump later posted a four-minute video of himself discussing the allegations, which he described as a “hoax” that amounts to election interference. ”I’m an innocent man. I did nothing wrong. I will fight this, just like we’ve been fighting for seven years.” he said.

Mr Trump’s attorney Jim Trusty told CNN the former president had received details of the charges in a summons document.

He said they include conspiracy, false statements, obstruction of justice, and illegally retaining classified documents under the Espionage Act.

The indictment arises from a months-long investigation by special counsel Jack Smith into whether Mr Trump broke the law by holding onto hundreds of documents marked classified at his Palm Beach property Mar-a-Lago and whether he took steps to obstruct the government’s efforts to recover the records.

Prosecutors have said the former president took roughly 300 classified documents to Mar-a-Lago after leaving the White House, including around 100 which were seized by the FBI in August during a search of the home that underscored the gravity of the Justice Department’s investigation.

The former president has insisted he was entitled to keep the classified documents when he left the White House and has claimed without evidence that he had declassified them.

It is the second indictment of Mr Trump - who has already been charged in New York on 34 counts of falsifying business records connected to “hush money” payments to porn actress Stormy Daniels and faces additional investigations in Washington and Atlanta that could lead to criminal charges.

Mr Trump and his team have long seen the special counsel investigation as far more perilous than the New York case - both politically and legally.

It remains unclear what the immediate and long-term political consequences will be for Mr Trump.

His first indictment spurred millions of dollars in contributions from angry supporters and did not damage Mr Trump in the polls as the 2024 presidential race ramps up.

Mr Trump’s legal troubles extend beyond the New York indictment and classified documents case.

The special counsel has a separate probe underway focused on efforts to overturn the results of the 2020 presidential election while the district attorney in Georgia’s Fulton County is investigating Mr Trump over alleged efforts to subvert the 2020 election in that state.

Meanwhile, Mr Trump’s lawyers have asked a judge in New York to reduce the five million dollars awarded to writer E Jean Carroll in a civil suit to less than one million dollars.

The payment was awarded by a jury in May for sexual abuse and defamation after E Jean Carroll had claimed the former president raped her in a department store in 1996.