Liberia's jailed ex-President Charles Taylor has started his appeal at a UN-backed special court in The Hague.
Last May, the court sentenced him to 50 years in prison for aiding and abetting rebels in neighbouring Sierra Leone during the 1991-2002 civil war.
Defence lawyers have called the verdict a "miscarriage of justice" and ask for the conviction to be quashed.
Last week Taylor, 64, reportedly wrote to MPs demanding a presidential pension of $25,000 (£15,600) in Liberia.
Describing the withholding of his state presidential pension as a "mammoth injustice", Taylor is quoted in the letter as saying that he is entitled to consular access and diplomatic services at The Hague, but he has been "denied that right".
Taylor became the first former head of state to be convicted of war crimes by an international court since the Nuremberg trials of Nazis after World War II.
Throughout his trial, the former Liberian leader, who was arrested in 2006, maintained his innocence.
The court was set up in 2002 to try those who bore the greatest responsibility for the war in Sierra Leone in which some 50,000 people were killed.
It found Taylor guilty on 11 counts of war crimes, relating to atrocities that included rape and murder, and described by one of the judges as "some of the most heinous crimes in human history".
In return for so-called blood diamonds, Taylor provided arms and both logistical and moral support to Sierra Leone's Revolutionary United Front (RUF) rebels - prolonging the conflict and the suffering of the people of Sierra Leone.
His lawyers have filed 42 grounds of appeal, arguing that the trial chamber's findings were based on "uncorroborated hearsay evidence".
"The colossal judgment, over 2,500 pages in length, is plagued throughout by internal inconsistencies, misstatements of evidence and conflicting findings," his lawyer Morris Anyah said in court papers quoted by the AFP news agency.
Prosecutors, meanwhile, are expected to argue that the court made a mistake by only convicting Taylor of aiding and abetting the RUF and its allies, the Armed Forces Revolutionary Council.
"The Trial Chamber erred in law and in fact by failing to convict Mr Taylor for ordering crimes committed by RUF/AFRC forces who were implementing his instructions," the prosecution said in court papers.
Taylor started Liberia's civil war as a warlord in 1989, and was elected president in 1997. He governed for six years before being forced into exile in southern Nigeria. He was arrested in 2006 while trying to flee Nigeria.
The trial was moved to the Netherlands due to concerns that the case might spark fresh instability in Sierra Leone and Liberia.