Boko Haram fighters have claimed the lives of some 400 people since April in Nigeria and Cameroon, according to a rights group.

The figure is twice the number of killings by the terrorist group in the previous five months.

Amnesty International group said in a statement on Tuesday that the increasing use of suicide bombers has killed at least 381 civilians in the two countries.

The rights group noted that the suicide bombers are often women and girls forced to carry and detonate explosives in crowded areas.

“Boko Haram is once again committing war crimes on a huge scale, exemplified by the depravity of forcing young girls to carry explosives with the sole intention of killing as many people as they possibly can,” said Alioune Tine, Amnesty International's director for West and Central Africa.

“This wave of shocking Boko Haram violence, propelled by a sharp rise in suicide bombings, highlights the urgent need for protection and assistance for millions of civilians ... Governments in Nigeria, Cameroon and beyond must take swift action to protect them from this campaign of terror.”

According to Amnesty International, at least 223 civilians have died in Nigeria since April. It also said the real death toll could be far higher.

“Between May and August, seven times more civilians were killed than in the preceding four months, while 100 civilians were killed in August alone,” it said.

Amnesty also said that in neighboring Cameroon, at least 158 civilians died in Boko Haram attacks since April. The figure is four times higher than the previous five months.