DOUALA, Cameroon (Reuters) - Two children carrying explosives blew themselves up on Friday near a camp in northern Cameroon housing civilians displaced by Nigeria’s Boko Haram militants, killing nine people and wounding 30, officials said.

They entered the town of Kolofata, around 10 km (6 miles) from the border with Nigeria, before dawn, posing as refugees looking for food before the start of the daytime fast for Ramadan.

“Two suicide bomber adolescents aged between 10 and 15 years infiltrated the town of Kolofata,” Communications Minister Issa Tchiroma Bakary told state radio, adding that both had detonated their explosives.

“The death toll is 1l, including the two suicide bombers, and 30 wounded, of which 10 are seriously wounded,” he added.

A local government official said the 10 gravely wounded had been transported to a hospital in a nearby town.

“It was unbearable. People were screaming. Others were moaning. It was total horror,” said a policeman present at the scene of the bombing.

Northern Cameroon has in recent years suffered from the overflow of violence linked to Nigeria’s Boko Haram Islamist insurgents. Nigerian refugees have flooded across the border and local residents have been forced to flee their homes.

Boko Haram launches frequent cross-border raids in its bid to carve out an Islamic caliphate. Its eight-year insurgency has killed more than 20,000 people in the Lake Chad region and, according to the latest U.N. refugee agency figures, displaced 2.7 million.

The agency said on Friday it was “stepping up its response as large numbers of refugees return from Cameroon to north-eastern Nigeria,” including some 12,000 in May, often returning home to very harsh, unsanitary conditions.

Villages and towns in the area have regularly been targeted by bombers. The officials said that Friday’s bombing came a day after two young girls detonated their explosives in the nearby village of Djakana, killing themselves and lightly injuring two members of a local civilian self-defense force.

Kolofata has repeatedly been struck in the past, including one attack that killed nine people in September 2015. Nigeria’s army has retaken much of the territory once occupied by Boko Haram, and a military coalition of regional neighbors has helped fight the Islamist insurgents across the borders in Niger, Chad and Cameroon.

The Cameroonian government has deployed thousands of soldiers, including elite units, to the Far North region.