The Boko Haram extremist group has killed over 300 civilians in Nigeria and Cameroon since April, revealed Amnesty International on Tuesday.
The rights group said that 381 people were killed in what it described as a resurgence of the extremist organization.
The spike in attacks by the extremists is a result of increased use of suicide bombers, often women and girls, who carry out the attacks in highly populated areas in Cameroon's Far North region and Nigeria's Borno and Adamawa states, the rights group said. Cameroon has experienced at least one suicide attack per week, it said.
Boko Haram has killed 223 civilians in Nigeria since April. Boko Haram suicide bombers have killed 81 people in Nigeria since the start of April, said Amnesty.
In Cameroon, the extremists have killed at least 158 people in the same period. That is also linked to a rise in suicide bombings, the deadliest of which killed 16 people in Waza in July, the rights group said.
The number of deaths since April 1 is more than double that for the preceding five months, Amnesty said.
“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’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 in the Lake Chad region."
The Nigerian military has repeatedly said Boko Haram has been “defeated”. But in recent months, it has carried out a string of lethal suicide bombings and other high-profile attacks on towns and an oil exploration team.
In Nigeria, the deadliest attack was in July, when the extremists abducted an oil exploration team with staff of the state oil firm and a university while they were traveling in a military convoy. Boko Haram killed 40 people and kidnapped three others, Amnesty said.
Nigeria and Cameroon's governments should take swift action to protect civilians in need of humanitarian assistance, it demanded. Boko Haram's increased attacks have made it difficult to carry out humanitarian operations.
"The international community should also rapidly scale up its commitment to provide life-saving humanitarian assistance to the millions in the region who need it," urged Tine.
Boko Haram extremists have been crossing into and attacking towns in neighboring countries, including Cameroon and Niger, that contribute to a regional military force trying to eliminate the insurgency.
More than 2.5 million people have been displaced or become refugees in the Lake Chad region - which includes Nigeria, Cameroon, Niger and Chad - while 7.2 million people lack secure access to food because of the conflict with Boko Haram, according to the United Nations.
The insurgency has left more than 20,000 people dead since it began in 2009.