He faces charges of four counts of crimes against humanity, including murder, rape, persecution and "other inhuman acts," the ICC said.
Gbagbo, 66, was handed over to the court on November 29 and arrived at its detention center in the Netherlands on Wednesday morning, according to its statement.
He had been under house arrest in Ivory Coast since April, when he was ousted with the help of forces from the United Nations and France.
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It is the first time in the ICC's history that a former head of state has been detained there, the BBC reported.
Gbagbo is also the first person to be charged in connection with the four months of violence in Ivory Coast that followed its presidential election in November 2010. Around 3,000 people are estimated to have died in the unrest.
According to ICC prosecutors, there are "reasonable grounds" to believe Gbagbo ordered his forces to attack civilians they accused of supporting his rival, Alassane Ouattara:
Allegedly, the attacks were committed pursuant to an organisational policy and were also widespread and systematic as they were committed over an extended time period, over large geographic areas, and following a similar general pattern. [...]
Mr Gbagbo, together with others, allegedly exercised joint control over the crimes, and made a coordinated and essential contribution to the realisation of the plan.
Supporters of Ouattara, who is now Ivory Coast's president, are also accused of atrocities.
The ICC must confirm it is investigating all crimes committed by all parties, said Amnesty International. The rights group is also urging the ICC to prosecute alleged crimes against humanity dating back to the outbreak of armed conflict in Ivory Coast in 2002.
The ICC's chief prosecutor, Luis Moreno-Ocampo, promised Gbagbo's arrest would be followed by others:
"Ivorian victims will see justice for massive crimes: Mr. Gbagbo is the first to be brought to account, there is more to come."
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