Prosecutors told the court that they would present the "double face" of the
accused, Thomas Lubanga, revealing the manipulative military commander who sought to hide behind a politician's mask.
"Lubanga made children train to kill, Lubanga made them kill and Lubanga let the children die ... in hostilities," prosecution lawyer Ekkehard Withopf said in his opening statement.
Lubanga stands charged with abducting children and forcing them to participate in attacks by the armed wing of his Union of Congolese Patriots (UPC) during wars that ravaged the Democratic Republic of Congo (DRC).
Thursday's hearing marked the first time prosecution lawyers have presented evidence in a case before judges at the ICC -- set up to try war crimes, crimes against humanity and genocide.
At the start of the hearing, Lubanga, wearing bright blue traditional African dress, introduced himself as the former UPC president.
Provisionally charged with three counts of war crimes, he has denied all accusations against him. His lawyer Jean Flamme asked to court to suspend the confirmation hearing for procedural reasons but the judges have not yet ruled on that request.
At a news conference on Wednesday Mr Flamme cast his client as a peace-loving politician -- an image hotly disputed by prosecutors.
"Lubanga has told you he was a politician. Lubanga however, is a man with a double face, and the prosecution will show his other face," Mr Withopf said.
The hearing also marked the first opportunity for the victims of Lubanga's alleged crimes to address an international court.
"We hope that the presence of the victims will remind the participants that this hearing is not an intellectual exercise between prosecutor and defence, but that the destruction of thousands of young lives will be at the centre of the discussions," Belgian lawyer Luc Walleyn, representing three Congolese families, told the court.
Lubanga, 45, and his militia have been named in connection with a long series of human rights abuses in the northeastern DRC region of Ituri where inter-ethnic fighting over gold mines and other resources has claimed more than 60,000 lives since 1999, according to humanitarian groups
"The practise of ... using children in warfare represents one of the most brutal and morally troubling crimes against the most vulnerable groups in times of war: children," deputy prosecutor Fatou Bensouda said.
When given the floor for his opening statement Flamme instead raised procedural issues that filled the rest of the court day.
The lawyer argued the confirmation hearing should be suspended because the court cannot hear the prosecution evidence until the ICC appeals chamber has ruled on a defence motion challenging the jurisdiction of the court. It also complained that it did not have enough time to prepare for the hearing. Mr Flamme will continue with his submissions Friday.
The confirmation hearing is set to run through November 28, after which the judges must determine whether Lubanga will become the first person to stand trial before the ICC. Their decision is expected in late January.
During the 12-day hearing prosecutors will present an overview of the evidence, including written testimony from six former child soldiers.
Based in The Hague, the ICC was created by a treaty in 1998 and formally came into being following its ratification in 2002 by more than 60 countries. More than 100 nations have now endorsed the treaty.
Lubanga is the only suspect in ICC custody.