Four civilians were killed in the remote north of Cameroon in a cross-border attack by Boko Haram militants, according to state radio.

Boko Haram, an Islamist militant group operating in northern Nigeria, has made several incursions into the hilly jungle region of neighbouring Cameroon in recent months. Cameroon has deployed troops to the border in an attempt to repel them.

The militants launched their first assault in the early evening on Thursday in the village of Assighassia near the city of Mokolo.

Cameroon's army responded, and two of the militants were killed and a Cameroonian soldier injured, state-run Cameroon Radio Television reported late on Friday.

"Two hours later, the terrorist group again attacked the village of Ganse, also close to Mokolo, and killed four civilians."

Officials in the defence ministry said on Saturday they had been informed of the clashes and were seeking to confirm the details.

More than 40,000 people have fled to Cameroon to escape Boko Haram attacks in northern Nigeria, according to the U.N. refugee agency UNHCR, leaving behind few but the elderly and the disabled in their villages across the border.

But once over the border they are still not safe and UNHCR is seeking to transfer many of them to a refugee camp further from the frontier at Minawao.

Foncha Ngeh, a businessman based in Cameroon's northern hub of Maroua, said that hundreds of people were fleeing from isolated border villages in Cameroon to bigger towns and cities in search of safety.

Boko Haram have killed hundreds of people this year, mostly in northeastern Nigeria, although they have launched attacks across the country.