A Ugandan border town where an attack on a school by suspected extremist rebels left 42 dead was preparing to bury its victims on Sunday.

One of eight people wounded in Friday night’s attack on Lhubiriha Secondary School – located just over a mile from the Congo border – had died overnight, Mpondwe-Lhubiriha mayor Selevest Mapoze said.

Security forces were said to be stepping up patrols along the frontier with volatile eastern Congo.

“Most of the relatives have come to take their bodies” from the morgue, he said.

Some students were burned beyond recognition, and others were shot or hacked to death, after militants armed with guns and machetes attacked the school, which is coeducational and privately owned.

Ugandan authorities believe at least six students were abducted, taken as porters back to Congo.

In addition to the 38 students who were killed, the victims included a school guard and three civilians.

UN secretary-general Antonio Guterres condemned the attack in a statement, urging “the importance of collective efforts, including through enhanced regional partnerships, to tackle cross-border insecurity between (Congo) and Uganda and restore durable peace in the area”.

The atmosphere in Mpondwe-Lhubiriha was tense but calm on Sunday, as Ugandan security forces roamed the streets outside and near the school, which was protected by a police cordon.

Ugandan security forces have not given a detailed account of how the rebels, active in eastern Congo, were able to carry out the attack.

The group, known as the Allied Democratic Forces, or ADF, rarely claims responsibility for attacks. It has established ties with the so-called Islamic State (IS) group.

In a statement released on Sunday, Ugandan president Yoweri Museveni described the attack as “criminal, desperate, terrorist and futile”, vowing to deploy more troops on the Ugandan side of the border.

The ADF has been accused of launching many attacks targeting civilians in remote parts of eastern Congo in recent years, including one in March in which 19 people were killed.

The ADF has long opposed the rule of Ugandan president Mr Museveni, a US security ally who has held power in the East African country since 1986.

The group was established in the early 1990s by some Ugandan Muslims, who said they had been sidelined by Mr Museveni’s policies.

At the time, the rebels staged deadly attacks in Ugandan villages as well as in the capital, including a 1998 attack in which 80 students were massacred in a town not far from Friday’s raid.

Students have been attacked because schools are considered soft targets, pupils are sometimes recruited into rebels ranks or used to carry food and supplies for insurgents, and such raids provide media coverage coveted by extremists.

The raid appears to have taken Ugandan authorities by surprise, with first responders arriving after the attackers had left.

Some villagers have moved away from the Mpondwe-Lhubiriha community temporarily, fearing more attacks, Mr Mapoze said.