Gibril Ealoghima Massaquoi is accused of murdering "disarmed soldiers" and civilians, recruiting child soldiers and rape between 1999 and 2003 when he held a senior position in the Revolutionary United Front, a Sierra Leone rebel group that fought in Liberia.

Arrested in March last year in Finland, where he has lived for the last decade, the suspect denies the charges, including, "aggravated war crimes" and "aggravated crimes against humanity", the state prosecutor said in a statement.

"The suspected crimes have breached generally recognised laws and rules of conflict as well as harming the wider protection of humanity," prosecutor Tom Laitinen said.

The charges carry a minimum sentence of eight years in jail but the court could also deliver a life term if convicted.

Police said the man, born in 1969, is suspected of committing the offences himself and inciting others to commit them.

An estimated 250,000 people died in the West African country's civil war, which raged from 1989-2003 and was marked by widespread mutilation and rape, often carried out by child soldiers overseen by warlords.

Finnish police opened investigations in 2018, interviewing dozens of people in Liberia and neighbouring Sierra Leone.

The case will be heard at Pirkanmaa district court in southern Finland, the prosecutor said.