• Former President Donald Trump said he has been told he is a target in the Jan. 6 criminal investigation by special counsel Jack Smith.
• Smith already has criminally charged Trump with about three dozen crimes related to retaining classified documents when he left the White House.
• Trump also suggested he may soon face indictment for the Jan. 6 probe.
• That investigation is focused on Trump's efforts to overturn his loss in the 2020 election to President Joe Biden.

Former President Donald Trump on Tuesday said he has been told he is a target in the Jan. 6 criminal investigation by special counsel Jack Smith.

Trump is the leading contender for the 2024 Republican presidential nomination. Smith already has criminally charged Trump with about three dozen counts related to retaining classified documents when he left the White House.

Trump also suggested he may soon face indictment for the Jan. 6 probe, which is focused on Trump's efforts to overturn his loss in the 2020 election to President Joe Biden. Trump posted his statement on his Truth Social account.

Two sources with direct knowledge of the probe confirmed to NBC News that Smith sent Trump a target letter in the case.

Such letters are sent by the Department of Justice to give people the chance to testify before a grand jury after the DOJ determines there is substantial evidence linking them to a crime.

"Deranged Jack Smith, the prosecutor with Joe Biden's DOJ, sent a letter (again, it was Sunday night!) stating that I am a TARGET of the January 6th Grand Jury investigation, and giving me a very short 4 days to report to the Grand Jury, which almost always means an Arrest and Indictment," Trump wrote on his Truth Social site.

Trump wrote that he was given what he called the "horrifying news" on Sunday evening by his lawyers.

A spokesman for Smith declined to comment.

A hearing in the classified documents criminal case is set for Tuesday in Florida federal court.

Trump's lawyers have asked that any trial in that case take place after the 2024 election. Smith's prosecutors oppose that bid.

Trump is separately under criminal investigation by a Georgia state prosecutor for his attempt to get election officials there to reverse his loss to Biden in Georgia.

A spokesman for Rudy Giuliani, the lawyer who led Trump's efforts to undo his 2020 election loss, said he has not received a target letter from Smith. Lin Wood, a lawyer and Trump ally, also said he has no received such a letter.

Timothy Parlatore, a lawyer for Bernard Kerik, the former New York City police commissioner who worked with Giuliani in the election reversal effort, told NBC that Kerik has not been given a target letter.

Follow our live coverage of Donald Trump's indictment for interference in the 2020 election.

- Additional reporting by CNBC's Kevin Breuninger