A former rebel commander accused of being involved in the killing of 18 civilians and other crimes that included rape and eating pieces of a school teacher's heart during Liberia's civil war appeared in a Swiss court room on Thursday.

The trial is just one of a handful of cases brought to international courts in connection with the West African country's 1989-2003 civil war, which became a byword for savagery and killed hundreds of thousands of people.

The defendant, 45-year-old Alieu Kosiah, denies the charges. His lawyer said Kosiah was not present in the area in question when the alleged crimes were committed.

Kosiah's crimes are listed by the Swiss court as "recruitment and use of a child soldier, forced transportation, looting, cruel treatment of civilians, attempted murder, murder (directly or by order), desecration of a corpse and rape".

Kosiah was one of the so-called 'big men' in the rebel faction ULIMO whose battalion fought against the troops of warlord Charles Taylor in the remote Lofa County in the 1990s.

The indictment says that he killed or participated in the killing of 18 civilians, forced a displaced woman to be his "wife", raping her repeatedly, and that he recruited a 12-year-old boy as his personal bodyguard.

In one incident described in the indictment, Kosiah joined fighters in eating slices of an assassinated man's heart off a metal plate. Acts of cannibalism were not uncommon in the conflict.

Kosiah, who has given testimony to Swiss prosecutors, has not yet pleaded in court and is due to be heard next week.

"According to Mr. Alieu Kosiah, one of the big problems with this case is he had not yet arrived in Lofa (county) at the time of the crimes he supposedly committed there," his lawyer Dimitri Gianoli told Reuters before the trial.

"(He) has always been very clear on his whereabouts in Liberia and the court filings include testimonies collected in Switzerland that confirm it."

The case is a first for Switzerland under a 2011 law allowing prosecution for war crimes committed anywhere.

Lawyers for Liberian victims are opposed to a court decision to postpone their hearings until next year due to COVID-19, effectively preventing them from hearing Kosiah in person.

The court is also mulling video link testimonies.

"After the unspeakable things they went through during the war they deserve to be present," said Alain Werner, a lawyer representing four plaintiffs, in a pre-trial interview.

Liberia has never prosecuted its war criminals despite a recommendation to do so by its Truth and Reconciliation Commission more than 10 years ago.