Jean-Pierre Bemba, formerly Vice President of the Democratic Republic of Congo, is in custody in Belgium after being arrested on a war crimes warrant from the International Criminal Court.
Mr Bemba was arrested in a Brussels suburb around 8pm yesterday.
The International Criminal Court is waiting for Belgian authorities to order his transfer to the court.
The tribunal expects Mr Bemba will go before a Belgian judge in the next few days and that he will be transferred to the ICC in a matter of weeks.
Mr Bemba was arrested on a warrant that listed four charges of war crimes and two of crimes against humanity, all allegedly committed in the Central African Republic.
The arrest warrant was issued on Friday, but was not made public.
It was the first warrant issued over the situation in the DRC, the ICC said.
But prosecutor Luis Moreno-Ocampo made it clear that the investigation is ongoing and it would not be the only warrant issued in the case.
Mr Bemba, 45, was one of four vice presidents in a transitional government in the DRC between 2003 and 2006.
The multi-millionaire businessman led the Movement for the Liberation of Congo (MLC) rebel group, which later converted itself into a political party.
In 2002, Mr Bemba's group was asked by former president Ange-Felix Patasse of the neighbouring Central African Republic to come into his country and put down a coup attempt.
Once that had been done, the 1,000-strong MLC force was accused of installing a reign of terror.
After President Patasse was ousted the following year, his successor pressed charges against Mr Bemba of rape and murder, though Mr Bemba consistently denied the charges.
Eventually the government of the Central African Republic referred the case to the International Criminal Court based in The Hague.
In recent months, Mr Bemba had been living in exile in Portugal after his defeat in Democratic Republic of Congo's presidential election in October 2006. He is facing charges of high treason in his country.
Mr Bemba is the fourth person to be arrested by the ICC. The others are Democratic Republic or Congo nationals being held for alleged atrocities they committed in that country.
The ICC is also conducting investigations into war crimes in Uganda and Sudan's Darfur region.
The ICC is the first permanent tribunal set up to try charges of genocide, crimes against humanity, and war crimes.
