AFP/Yaoundé

 At least seven civilians were killed Friday in a suicide attack in Kolofata, northern Cameroon, a region where Nigeria's Boko Haram Islamists are highly active, local officials said.

"A suicide bomber went to a place selling doughnuts and blew up," a regional security source told AFP. 

"We have eight dead at the site, including the bomber," the source said, without stating whether the attacker was male or female. 

Another source also confirmed details of the attack and gave the same toll. 

Kolofata, which lies 10 kilometres (six miles) from the border with Nigeria, is located in a region of the same name which has been regularly targeted by Boko Haram extremists. At least seven people were killed in a double suicide attack on the town in September. 

It is close to Kerawa, another town on the Nigerian border where between 20 and 40 people lost their lives in a September 3 double suicide bombing -- one of the deadliest attacks on Cameroonian territory.

Since July, Cameroon's far north has been hit by a series of attacks blamed on Nigeria's Boko Haram which earlier this year pledged allegiance to the Islamic State group.

The Kolofata attack came as Cameroonian troops have been sweeping the border area in order to weaken the jihadists who are very active in northeastern Nigeria and the far north of Cameroon. 

Cameroon, Chad and Niger have formed a military alliance with Nigeria and Benin to battle the extremists, who this year declared allegiance to the Islamic State.

The Islamists' grip on the region has suffered as a result of offensives launched by local armies. 

Last week, Cameroon claimed its troops had dealt a major blow to Boko Haram, killing around 100 fighters and freeing 900 hostages in a three-day operation at the end of November. 

Over the past year, Boko Haram has stepped up cross-border attacks in Niger, Chad and Cameroon while also continuing to mount shooting and suicide assaults on markets, mosques and other mostly civilian targets within Nigeria itself. 

For many years there was little to no surveillance of the border with Nigeria by Cameroon, enabling the jihadists to use the remote region as a rear base to stock its weapons, vehicles and supplies. 

But Cameroon, which is part of a regional coalition helping Nigeria combat the jihadists, now has stepped up border surveillance.