A UN panel has given Senegal 90 days to put former Chad President Hissene Habre on trial or send him to Belgium to face trial for alleged human rights abuses.
The United Nations Committee Against Torture said Senegal had broken international human rights rules by not dealing with Mr Habre for 15 years.
Last year, a Senegalese court ruled that it did not have the power to decide whether he should be extradited.
Senegal then referred the case to the African Union, which is still to rule.
Mr Habre is wanted in Belgium for alleged abuses committed under his rule between 1982 and 1990.
Alleged victims filed complaints under Belgium's universal jurisdiction law, which allows judges in Brussels to prosecute human rights offences anywhere.
Reed Brody of the lobby group Human Rights Watch, who also acts as a lawyer for Mr Habre's alleged victims, welcomed the UN panel's decision.
"This ruling means that Senegal cannot allow Hissene Habre to escape justice," he said.
"The UN decision puts the law back into a case that was becoming a political soap opera."
Mr Habre's administration has been accused of murdering and torturing political opponents.
He denies any knowledge of atrocities.
After being deposed by rebels in 1990, Mr Habre went into exile in Senegal.
BBC Africa analyst Elizabeth Blunt says some of Mr Habre's alleged victims have fought a dogged campaign to get him prosecuted.
In 2001, a Senegalese court ruled that it did not have jurisdiction to try Mr Habre on war crimes charges.
The African Union committee on the case is due to meet next Monday, and put its recommendations to the organisation's summit at the beginning of July.