Cameroonian troops attacked Boko Haram extremists in Borno state, killing several of the militants and destroying some of their equipment, a military official said Monday.

The forces entered Nigeria after residents of Ndaba in Borno state said Boko Haram militants were massing in the hills around the village and planning an attack, said Col. Jacob Kodji.

Several militants were killed in the fighting Thursday and Friday near Ndaba, about 20 kilometers (12 miles) from the Cameroonian border, said Kodji. He would not give an exact number of casualties and did not say whether any Cameroonian forces were killed or wounded. Other militants fled and some may be hiding out in Ndaba, he said.

Cameroonian troops also destroyed some of the militants’ vehicles and ammunition, he said.

Boko Haram, which is based in the north of the country, has been waging a six-year insurgency to create an Islamic state. Borno state is one of its strongholds.

The militants killed an estimated 10,000 people last year and are blamed for the abduction last April of more than 200 schoolgirls who remain missing.

In response to increasing attacks in Nigeria and in neighboring countries, Cameroon, Chad and others have banded together to fight the extremists.