At least 42 people were killed and eight others critically injured in a suspected rebel attack on a secondary school in western Uganda, police and local authorities said on Saturday.
A regional government official told dpa that 15 children were also abducted.
The Allied Democratic Forces (ADF), a militia linked to the Islamic State group, were blamed for the carnage that took place on Friday night in the town of Mpondwe, located near the border with the Democratic Republic of Congo.
The Ugandan army said it was pursuing the militants and would retaliate.
United Nations Secretary-General António Guterres condemned the attack, according to a spokesperson, calling for those responsible to be brought to justice.
EU foreign affairs representative Josep Borrell echoed his comments, calling the attack “appalling.”
“This terrorist violence targeting children is beyond comprehension,” Borrell said in a tweet.
There have been attacks by the ADF and other Congolese militias in the border area of the two East African countries for years.
The ADF says it is fighting for the rights of Muslims, who are increasingly pushed to the margins of Ugandan society by the government and law enforcement.
The group’s goal is the overthrow of the government in Kampala.
However, the victims of their attacks are mostly civilians.
The group’s worst attack occurred in 1998, when militants killed 80 students in an attack on a university in the border region.