Lawyers for former Liberian President Charles Taylor are challenging his war crimes indictment at the United Nations-backed tribunal in Sierra Leone.

The challenge was made as the court started a week-long appeals session Friday for those who have been indicted.

A spokesman for the court, Peter Anderson, says the appeals chamber has to rule on certain legal issues before trials could begin next year.

"There are certain questions of law that are going to have to be cleared up before they can proceed," he said. "For example, the former president of Liberia, Charles Taylor, is contesting the indictment against him on the grounds that he had immunity as head of state and on the grounds of extra-territoriality, that is to say that Liberia is outside of Sierra Leone and he will say that the court's mandate doesn't extend to Liberia."

Mr. Taylor is living in exiled luxury in Nigeria, where the government has promised to protect him from arrest as long as he does not meddle in Liberian affairs. Some experts in Liberia say he has been doing just that ever since he left.

Under international pressure, Mr. Taylor left Liberia in August, saying he was sacrificing himself to end Liberia's civil war, but that he was innocent of any wrongdoing.

The war crimes tribunal indicted Mr. Taylor in June, accusing him of bearing the greatest responsibility for attrocities committed during the 10-year war in Sierra Leone, which ended in 2001, by allegedly backing rebels in exchange for illegally mined diamonds.

Independent human rights activist and consultant Ian Smillie says Mr. Taylor must stand trial to ensure lasting peace in West Africa. He accuses Mr. Taylor of fueling instability throughout West Africa, by trading in weapons, diamonds and illicit timber.

"As long as Charles Taylor is at large, nobody in West Africa can sleep safely at night," Ian Smilie. "If you remember that his parting words to Liberians were that he would be back. I think it's absolutely essential as a message to other people like him in the world, to other tyrants, but also to the people who suffered so much from the trouble in Liberia and in the region at his hands, that he be surrendered by the government of Nigeria to the special court in Freetown, and that he answer for some of the charges that have been laid against him."

Liberia's new transitional leader Gyude Bryant has also called on Mr. Taylor to answer the charges at the court in Freetown, saying it would be honorable to do so.

The court has indicted 12 others on various charges of war crimes, crimes against humanity and other violations of international humanitarian law.

Two of them are dead, rebel leaders Foday Sankoh and Sam Bockarie, while former Sierra Leone military leader Johnny Paul Koroma and Mr. Taylor are still at large. Nine other defendants are in custody in Sierra Leone.

Among those in custody, several are also appealing their indictment. Lawyers for Sierra Leone's former Internal Affairs Minister Sam Hinga Norman say he cannot be charged with recruiting child soldiers because they say this is not an offence under international law. But human rights groups disagree.