France has promised to facilitate the trial of Chad's ex-President Hissene Habre, who lives in exile in Senegal.
Hissene Habre's regime is accused of widespread murder and torture
"We have to help Senegal financially, technically, legally to deal with the case," French President Nicolas Sarkozy said on a visit to Senegal.
Mr Habre, dubbed "Africa's Pinochet", faces charges of human rights abuses during eight years in office.
He fled to Senegal in 1990. Last year the African Union (AU) asked for him to be prosecuted there.
Mr Habre, who is in his 60s, was deposed in an uprising led by the current President, Idriss Deby, and denies knowledge of the alleged murder and torture of political opponents.
A commission of inquiry said his government was responsible for some 40,000 politically motivated murders and 200,000 cases of torture in the eight years he was in power.
"That a dictator is brought to trial to answer for his actions is already good news," French radio quotes Mr Sarkozy saying at a press conference with his Senegalese counterpart Abdoulaye Wade.
"That the court in charge of the trial will be made up of Africans and will take place in Africa is another piece of good news."
Mr Wade acknowledged France's pledge and called for more international help, AFP news agency reports.
"This trial will cost a lot of money, I think that it should be the international community which should see to its financing," he said.
Mr Sarkozy is on his first visit to sub-Saharan Africa since becoming president in May and is due to go to oil-rich Gabon on Friday.
Correspondents say he is trying to encourage support for his idea of what he has called a "EurAfrican" partnership for Europe and Africa: urging the two continents to find a new way of working together, free from much of the colonial baggage of the past.