Cameroon has condemned 89 suspected Boko Haram operatives to death for "terrorism" since the start of 2015, a judicial source said Friday.

The sentences come after Cameroon adopted a controversial anti-terror law in December 2014 allowing capital punishment for those found guilty of carrying out terror attacks or complicity in terrorism. 

Those convicted were mostly arrested on Cameroon's border with Nigeria, the birthplace of the extremist group that has pledged allegiance to the Islamic State (IS) group.

Cameroon already had the death penalty for murder, but there have been no executions since the mid-1980s.

Almost 850 people suspected of links to Boko Haram are being held in prison in Maroua, capital of the far north of Cameroon. 

They include Nigerians and Chadians as well as Cameroonians, according to regional newspaper L'Oeil du Sahel.

Boko Haram violence has left at least 17,000 dead and forced more than 2.6 million from their homes since 2009.

And nearly 1,200 people have been killed since the Nigerian fighters took their offensive into Cameroon in 2013, according to government figures.

In recent years, Boko Haram fighters slipped back and forth across the frontier, often using Cameroon's remote north as a rear base, acquiring arms, vehicles and supplies there.

But since late November, the Cameroon army has carried out operations in several border areas aimed at weakening the Nigerian jihadists. 

As a result, the insurgents turned away from direct confrontation with the military in favour of suicide attacks, increasingly carried out by women and girls.