At least 15 people have been killed in an attack by suspected Boko Haram militants on a bus in northern Cameroon, a senior local security official and a businessman said on Saturday.

Over the last year, Boko Haram, which has killed thousands in its struggle to create a caliphate in northern Nigeria, has stepped up attacks on both sides of the border, forcing Cameroon to dispatch thousands of troops to its north.

"Boko Haram elements on Thursday attacked a bus that was transporting many passengers from Kousseri to Maroua and killed 25 persons on the spot," said a senior officer in the military's BIR rapid reaction unit deployed in the region.

The officer, who asked not to be named, said another 10 people had been severely injured and taken to Maroua hospital and he feared the death toll would rise.

Maroua is the capital of the Far North region, which has seen the worst of the spillover of Nigeria's conflict.

Cameroonian authorities were not available for comment on the attack, which took place in the evening of January 1. However, a local businessman based in the north said travelers who reached the town of Maroua had confirmed the incident.

Foncha Ngeh, who is based in Maroua, said travelers had told him there were at least 15 dead in the incident but many more had been injured and were being transported to Maroua for treatment.

Ngeh said there had been a string of other attacks in the region, carried out by Islamists but also ordinary bandits targeting people traveling during the holidays with lots of cash.

Late last month, Cameroon had to call on its air force to help troops dislodge Boko Haram fighters who briefly occupied a military camp after hundreds of militants mounted a wave of attacks on five northern towns.

Raids by Boko Haram have forced many Cameroonians living along the porous border to abandon farms, raising the risk of food shortages in the semi-arid part of the country.