The United Nations human rights chief has asked Senegal to reconsider its decision to extradite former Chadian President Hissene Habre to his homeland.

In a statement issued Sunday, Navi Pillay says that Senegal, as a party to the Convention Against Torture, may not extradite anyone to a state “where there are substantial grounds for believing he would be in danger of being subjected to torture.”

Mr. Habre, who was ousted in a coup in 1990 by current Chadian President Idriss Deby, already has been sentenced to death in absentia for the torture and killing of political opponents. He has lived in Senegal since the coup.

Ms. Pillay said Senegal needs to obtain guarantees of a fair trial from the Chadian government. She said sending Mr. Habre home without those guarantees “may amount to a violation of international law” because he could be subjected to torture or killed without a trial.

Senegal announced Friday that Mr. Habre would be extradited on a charter flight Monday.

During over a decade of wrangling over where he should stand trial, Senegal said at first it did not have the jurisdiction to hold a trial, and then that it lacked the funds. In 2005, a Belgian judge issued an international arrest warrant charging Mr. Habre with crimes against humanity.

Several human rights groups also have expressed concern about Senegal's decision. Alioune Tine, who is president of the African Human Rights Organization, said you cannot send someone to a country that practices torture and uses the death penalty.