The Cameroonian army killed 143 Boko Haram militants who attacked a military base in Kolofata, north of the country on Monday, the government said, adding that one soldier had also died in the fighting.

The toll was “the heaviest loss yet” suffered by the Nigeria-based Boko Haram group on Cameroonian soil, Communications Minister and government spokesman Issa Tchiroma Bakary said in a statement read out on television and radio.

He said the attack began in the early hours when “several hundred” Islamist fighters took advantage of thick fog to cross over from Nigeria and tried to storm the town’s military base, where an elite army unit is stationed.

Intense fighting erupted near the base, lasting for more than five hours before the attackers fled back towards the border, the spokesman said, adding that the army had seized a significant arsenal of heavy weaponry from the militants.

A local source said that residents fled “as soon as people heard the first gunfire” in the town.