Nigerian courts convicted 125 Boko Haram Islamist militants and financiers of a series of terrorism-related offences in a mass trial this week, the attorney-general's office said.

A Boko Haram insurgency has killed thousands of people and displaced millions since it began in 2009, creating a humanitarian crisis in northeastern Nigeria and putting pressure on the government to bring the conflict to an end.

Kamarudeen Ogundele, the spokesman of the Attorney-General's office, said in a statement late on Friday that "they were convicted of charges bordering on terrorism, terrorism financing, rendering material support, and cases relating to International Criminal Courts (ICC) criminality".

The last mass trials of Boko Haram suspects took place between 2017 and 2018, where 163 people were convicted and 887 set free.

Ogundele added that from the previous convictions, 400 defendants who had completed their sentences were moved to a rehabilitation centre known as Operation Safe Corridor in Gombe State, northeast Nigeria "for rehabilitation, deradicalisation and subsequent reintegration".

Boko Haram kidnapped more than 270 girls from a school in the northeastern town of Chibok in April 2014, an attack that sparked outrage and gave rise to the global "#Bring Back Our Girls" campaign, though more than half of the girls have returned, many as mothers of multiple children.

The breakdown of the latest convictions showed that 85 peeople were convicted for terrorism financing, 22 for ICC related crimes, while the rest were convicted for terrorism.