Alieu Kosiah, a former rebel commander accused of being involved in the murder of civilians, rape and consuming pieces of a teacher's heart during the civil war in Liberia has denounced his lengthy pre-trial detention as proceedings began on Thursday in Switzerland.

The lawsuit is one of the few cases brought before international courts in connection with the 1989-2003 civil war in the country, in which hundreds of thousands of people were killed.

The accused, Alieu Kosiah, 45, denies the charges. His lawyer said Kosiah, who was arrested in Switzerland in 2014, was not present in the area when the alleged crimes were committed.

Liberian journalist Rodney Sieh witnessed the first day of proceeding in the court.