Boko Haram are ramping up fatal attacks on soft targets across West Africa, forcing almost 800,000 people to flee their homes since June, and stretching humanitarian efforts to breaking point, aid agencies and experts said on Friday.

More than 2.1 million people — or 300,000 households — have been uprooted in northern Nigeria since the Islamist militant group launched an uprising in 2009, according to data from the International Organization for Migration.

The insurgents scattered earlier this year after an army counter-offensive, but have since returned to a strategy of selective attacks in which they have bombed or fired on public places such as markets and places of worship.

The group has launched cross-border attacks, triggering displacement and hunger in neighboring Chad and Niger.

A double suicide bombing killed 19 people and wounded 143 on Thursday in northern Cameroon, where soldiers are battling Boko Haram fighters from Nigeria, military and local government officials said.

IHS Senior Africa Analyst Murtala Touray told VICE News that Thursday's attack is part of "escalating and expanding attacks" by Boko Haram, aimed at creating "serious humanitarian emergencies in the Cameroon, Chad, Niger and Nigeria."

The attacks targeted the town of Kerawa, the scene of clashes between the militants and government soldiers in February.

"The first (explosion) was just after 9 o'clock (4am ET) in the market in Kerawa and the other around 200 meters (218 yards) from the infantry camp," said an army officer based in the region.

Both the attacks were carried out by female suicide bombers according to a local government official. Some sources reported the death toll as higher than 30.

The escalation in neighboring nations is widely seen as retaliation for their involvement in a multi-national offensive against the group earlier this year, which dislodged Boko Haram from much of its territory. The group officially declared war on the state of Cameroon in February of last year.

Col. Didier Badjeck, a spokesman for Cameroon's military, suggested this attack is evidence of Boko Haram changing tactics, "They find it hard these days, coming face-to-face with our forces," Badjeck claimed, "What they do now is come in from Nigeria, attack border areas, and then run back to Nigeria."

Analyst Touray disputed this to VICE News, however, stating that "Boko Haram has used the same tactics all along," consisting of raids on military targets, car bombs, and suicide attacks on crowed areas. Touray warned that "the group will continue to focus on soft targets including transport hub, crowded areas… and can embarrass the government of Cameroon, Chad, Niger, and Nigeria."

No one has claimed yet responsibility for Thursday's bombings but they have the hallmarks of a Boko Haram attack. The Islamist fighters were blamed for a series of suicide bombings in the town of Maroua, also in Northern Cameroon, that killed dozens of people in July.

Female suicide bombers were also behind several blasts in northern Cameroon in July causing the regional governor to ban the Islamic veil as part of counter-terror measures.

Boko Haram's use of female bombers has become more frequent since the first recorded attack in June 2014 on a military barrack in Gombe state in northeastern Nigeria.