NIAMEY (Reuters) - Eighty-one people accused of fighting for Boko Haram went on trial in Niger on Thursday in a public court sitting, one of the first of its kind after closed-door trials of suspected insurgents were criticized by human rights groups.

Those on trial in a special international court in the capital Niamey come from Niger, Nigeria and Chad and are suspected of playing a role in Boko Haram’s near decade-long bid to create a caliphate in Nigeria.

The Islamist insurgency has spread beyond its roots in Nigeria, killing 20,000 and uprooting nearly 3 million in the Lake Chad region.

The Niamey trials follow closed-door Boko Haram trials, including in Nigeria where a court in October jailed 45 people to between three and 31 years in jail, but the government did not say what they were convicted of.

Open trials are meant to show that suspected fighters will be given due process, and could also help alleviate a conflict that has been stoked at times by the mistreatment of captives.

The death in 2009 of Boko Haram founder Mohammed Yusuf in police custody is seen as one of the major triggers for the conflict.

The Niamey court will hear 22 separate cases over the next 10 days, following the trial of nearly 300 people on similar charges last year. In all, nearly 1,000 people are expected to come before the court.