A federal grand jury has indicted Donald Trump for withholding classified government documents and obstruction of justice, the former US president's lawyer and another knowledgeable source said today.

It is the first federal indictment in US history against a former president.

The indictment, filed by the Justice Department, represents another legal challenge for Trump, who wants to return to the White House next year.

He was recently indicted in New York on 34 counts of concealing an extramarital affair during the campaign and is the subject of investigations in Washington and Atlanta that could result in criminal charges.

Trump has already announced on social media this morning that he must appear in a courtroom in Miami on Tuesday.

"I am an innocent man," Trump wrote on the "Truth" platform.

A spokesman for special counsel Jack Smith, the Justice Department official who led the investigation, declined to comment on the news because it is illegal for the government to comment publicly on a sealed grand jury case.

An anonymous source told British media that the indictment contains seven counts, and Trump's lawyer, Jim Trusty, told CNN that the charges include conspiracy, perjury, obstruction of justice and illegal possession of secret documents under the Espionage Act.

The lawyer expects to receive an insight into the indictment by Tuesday.

The Justice Department has been investigating whether Trump mishandled classified documents after he left the White House in 2021.

After searching his Mar-a-Lago property in Palm Beach, Florida, nearly a year ago, investigators seized about 13.000 documents, 100 of which contained classified information that had to be protected.

Trump previously defended himself by claiming that those documents are no longer classified because he declassified them as president, but offered no evidence of that.

Trump was the president of the United States from 2017 to 2021, and is the favorite for the Republican presidential nomination. He claims he is the victim of a politically motivated witch hunt and accuses the Justice Department of bias.