Judges cleared 73-year-old Gbagbo on Tuesday on charges of crimes against humanity relating to a wave of violence after disputed elections in 2010, and ordered his immediate release.
The crisis claimed some 3,000 lives.
But prosecutors at the Hague-based court challenged the release of Gbagbo, who has already spent seven years in jail, saying he should be detained while they make a broader appeal over his acquittal.
“The detention of Mr Laurent Gbagbo… shall be maintained pending the consideration of the present appeal” against his release, the ICC’s appeals judges said in a statement.
They will hold a fresh hearing on February 1 “in order to hear further submissions on the appeal.”
Judges made the same order for Gbagbo’s co-defendant and right-hand man Charles Ble Goude.
Prosecutors had argued that there was a “concrete” risk the Ivorian pair fail to return to the ICC if a subsequent appeal overturned Tuesday’s decision to acquit them.
Gbagbo’s daughter has said he intended to return to the Ivory Coast if released.