Two former Congolese militia leaders have been transferred from the Netherlands to a prison in the Democratic Republic of Congo (DRC).
Thomas Lubanga and Germain Katanga are the first ICC convicts to be allowed to serve sentences in their home country.
Former warlord Lubanga is serving 14 years for his crimes, while militia chief Katanga is due to be released in 2016.
The ICC says it will help supervise their imprisonment in the DRC.
Lubanga and Katanga "have both expressed a preference to serve their respective prison terms in DRC, their country of origin", the court said in a statement.
Their detention in the DRC must conform to international norms on the treatment of prisoners, it said.
Lubanga was once one of the most feared rebel leaders in the gold-rich northeastern Ituri region of the DRC.
He was found guilty of abducting children as young as 11 and using them to fight his battles.
Katanga was convicted for his involvement in a bloody massacre that left hundreds of villagers dead.
Last month, the ICC cut Katanga's 12-year prison term after he voiced regret and for good behaviour.
But Lubanga's request for early release was rejected by the ICC as "unjustified".
The ethnic conflict in Ituri between 1999 and 2003 is estimated to have killed 50,000 people.