Donald Trump has said he expects to be arrested by a federal inquiry into the US Capitol riot and efforts to challenge the 2020 election results.

The ex-president said in a social media post he had been informed by special counsel Jack Smith on Sunday night that he was a target of their investigation.

Mr Trump posted he had been told to report to a grand jury, "which almost always means an Arrest and Indictment".

The special counsel has not commented on Mr Trump's statements.

Such an indictment would be Mr Trump's third for alleged criminal offences, including 37 counts brought by Mr Smith's team in June accusing the president of mishandling classified documents.

Mr Trump has also been charged in New York City with falsifying business records in 2016 hush money payments to adult film star Stormy Daniels.

He is due to stand trial in that case next March, while a date for the classified documents case is still being contested by the president's lawyers.

Speaking in Cedar Rapids, Iowa, on Tuesday night, the former president expressed his frustration at the latest development.

"I didn't know practically what a subpoena was and grand juries and all of this. Now I'm becoming an expert, I have no choice because we have to," he said at the campaign event. "It's a disgrace."

Earlier in a post on his Truth Social platform, Mr Trump claimed that he had been sent a letter "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".

Mr Smith was appointed special counsel by US Attorney General Merrick Garland shortly after Mr Trump announced his presidential campaign last autumn.

His team was tasked with investigating Mr Trump's handling of classified documents after leaving the White House and with managing a sprawling federal investigation into the riot at the US Capitol and attempts by Mr Trump and his advisers to "interfere with the lawful transfer of power following the 2020 presidential election".

The special counsel's office has not discussed what specific criminal violations they are considering. It is not known if others have been told they are a target.

Last December, a House committee investigating the events of January 6 recommended four separate criminal charges be brought against the former president and his associates:

The Democratic-led committee - which included two Republicans - described the criminal referrals as a "roadmap to justice", but prosecutors do not have to follow a congressional committee's recommendations.

Mr Smith's own investigation has involved interviews with dozens of top Trump administration officials and advisers, including former Vice-President Mike Pence and Trump lawyer Rudy Giuliani.

According to public comments by some who have testified before the grand jury, questions have focused on efforts by Mr Trump's team to organise slates of "fake electors" who would claim that the former president had defeated Democrat Joe Biden in seven key battleground states.

State prosecutors in Atlanta, Georgia, are also investigating the former president on similar grounds, focusing on whether he illegally pressured state officials there to discard Mr Biden's victory. In a December 2020 phone call with Georgia Secretary of State Brad Raffensperger, Mr Trump asked that Georgia officials "find 11,780 votes" that would flip the state to Mr Trump.

A decision by Georgia prosecutors on whether to indict Mr Trump is expected next month.