Defence lawyers for Laurent Gbagbo have urged International Criminal Court judges to rule that they have no authority to put the former Ivory Coast president on trial on charges including murder, rape and persecution.
Lawyer Dov Jacobs told judges that Gbagbo is under investigation in the Ivory Coast for his role in violence that left some 3,000 people dead in the aftermath of the country's disputed 2010 presidential election and that authorities in his homeland should be the ones to try him.
"The defence urges the chamber to declare this case inadmissible," Mr Jacobs said as a crucial pre-trial hearing opened at the world's first permanent war crimes tribunal.
Gbagbo, wearing a suit and tie, sat silently in court listening to proceedings through a headset and made no immediate comment. He is the first former head of state to appear before judges in the court's 10-year history.
The hearing, scheduled to last until February 28, is designed to allow judges to assess a summary of prosecution evidence and decide whether it is strong enough to merit sending Gbagbo to trial.
Prosecutors were to begin outlining their case against the 67-year-old former history professor later and continue on Wednesday.
Prosecutors say Gbagbo and his supporters plotted to target supporters of current Ivory Coast President Alassane Ouattara in violence that erupted after Gbagbo refused to accept defeat in the 2010 election.
Gbagbo, who is charged as an "indirect co-perpetrator", insists he is innocent.
He was arrested in the Ivory Coast in April 2011 by forces loyal to Mr Ouattara and extradited to The Hague eight months later.
Some 300 supporters demonstrated outside the court, chanting "Free Gbagbo" and insisting that he is their country's rightful ruler and not Mr Ouattara.
The court's judges have already ruled that they have jurisdiction to hear the case, but a case can be ruled inadmissible if the Ivory Coast is investigating or prosecuting Gbagbo for the same alleged offences.
The Hague-based tribunal is a court of last resort, which only tries crimes if countries are unwilling or unable to prosecute them.
"Ivory Coast is neither unable nor unwilling to prosecute president Gbagbo," Mr Jacobs said.
Human rights activists welcomed the start of the hearing, but also used the occasion to urge the court to press charges against supporters of Mr Ouattara allegedly involved in months of post-election violence that left some 3,000 people dead in a country once known as one of West Africa's most stable democracies.
"Holding Gbagbo to account is a critical step for victims in (Ivory Coast)," Param-Preet Singh, senior international justice counsel at Human Rights Watch, said in a statement. "But the slow pace of investigations against pro-Ouattara forces feeds the perception that the ICC is going along with victor's justice."
While Gbagbo is in a jail cell in The Hague, his wife Simone, who also has been charged by the ICC in the post-election violence, remains in custody in the Ivory Coast, where officials have charged her with crimes including genocide.