“Our forces are pursuing the enemy to rescue those abducted and destroy this group,” defence spokesperson Felix Kulayigye said on Twitter.

Authorities did not say how many people had been abducted by the attackers, members of the rebel group Allied Democratic Forces (ADF) that has pledged allegiance to Islamic State.

The assailants attacked Lhubirira Secondary School in the western border town of Mpondwe late on Friday, burning a dormitory and looting food, police said.

“So far 25 bodies have been recovered from the school and transferred to Bwera Hospital. Also recovered are eight victims, who remain in critical condition at Bwera Hospital,” police said on Twitter.

Police did not say how many of the dead were schoolchildren.

The attackers fled towards Virunga National Park in Congo, police added.

The ADF rebels launched their insurgency against President Yoweri Museveni in the 1990s from an initial base in the Rwenzori Mountains.

The group was largely defeated by the Ugandan military but remnants fled across the border into the vast jungles of eastern Congo from where they have since maintained their insurgency - perpetrating attacks on civilian and military targets in both Congo and Uganda.

In April, the ADF attacked a village in eastern Democratic Republic of Congo, killing at least 20 people.