Ex-Malawian President Bakili Muluzi has been arrested, accused of stealing $11m (£7.7m) in donor money, says the country's Anti-Corruption Bureau.
The ACB said Mr Muluzi had been charged on 80 counts of allegedly siphoning aid cash into his private account.
The former president is due to appear at a court in Blantyre, where hundreds of his supporters have gathered.
Mr Muluzi, a candidate in May polls, denies any wrongdoing and has disputed the legality of the ACB investigation.
The BBC's Raphael Tenthani in Blantyre says the ex-president was arrested after appearing at the anti-graft bureau on Thursday morning to answer the allegations against him.
'Right to remain silent'
He says around 50 armed police and nearly 1,000 supporters of Mr Muluzi, who is not in custody, have gathered outside the magistrates' court in the city.
The former president's lawyer Jai Banda told AFP news agency his client had "exercised his right to remain silent" when questioned by the ACB.
Mr Muluzi, who ruled the poor southern African nation from 1994 to 2004, was first arrested over the allegations in 2006 but the then-director of public prosecutions threw out the charges.
His supporters say the case is politically-motivated to stop him standing in the forthcoming presidential election.
The inquiry comes amid concern that violence could flare before the forthcoming presidential election.
The former presidents of Mozambique, Joacquim Chissano, and Ghana, John Kufuor, were in Malawi on Wednesday to try to calm tensions.
Henry Mvula, Mr Muluzi's aide, earlier told the BBC's Network Africa programme the former Malawian president had nothing to hide and dismissed the case as a witch-hunt.
He said it was "meant to keep someone so busy within the context of the courtroom" in a "typical African way of running away from competition".
Malawi political analyst Rafiq Hajat told Network Africa: "If a court case is initiated against a candidate, their candidacy is immediately put into doubt. I think the political stratagem is fairly obvious."
Opposition United Democratic Front leader Mr Muluzi plans to stand in May against current head of state, Bingu wa Mutharika.
Mr Mutharika was Mr Muluzi's hand-picked successor but soon after he was elected, the pair fell out and Mr Mutharika formed his own party.