In western Uganda, fighters with ties to the Islamic State (IS) killed around 40 students at a school.
On Friday night at about 23:30 (Friday evening GMT), five militants assaulted the Lhubiriha secondary school in Mpondwe.
They allegedly broke into student dorms, lit fires, and killed and injured students inside with machetes.
The Democratic Republic of the Congo-based Allied Democratic Forces (ADF) have been accused, and a manhunt has begun.
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The majority of the more than 60 students at the institution are locals.
The communications minister of Uganda confirmed the deaths of 37 students, but did not specify how old they were.
According to Chris Baryomunsi, who spoke to the BBC on behalf of the victims' families, 20 were killed by machete attacks and 17 by fire.
The Ugandan army said that in addition to the teacher, a school guard and three community members were killed by the rebels.
After the machete attack, the rebels allegedly dropped a bomb into the hostel, according to the survivors. There may have been a fire in the structure, but it's unclear if this is the cause.
He also said that the rebels kidnapped six pupils to help transport the food they stole from the school's pantry. After that, the extremists crossed back into the DR Congo.
DNA testing will be required to identify some of the bodies because of the extensive burns they sustained.
After the incident, eight persons are still in serious condition.
Secretary General of the United Nations Antonio Guterres blasted the attack as a "appalling act" and demanded that those responsible be held accountable.
The Virunga National Park in the Democratic Republic of the Congo is home to some of the rarest species on the continent, including the critically endangered mountain gorilla.
The large area, which borders Uganda and Rwanda, is used as a safe haven by a variety of militias.
Defense spokesperson Felix Kulayigye tweeted, "Our forces are pursuing the enemy to rescue those abducted and destroy this group."
The Ugandan army has sent in helicopters to help locate the insurgents as they traverse the rugged landscape.
In order to deter attacks by the ADF, the two countries have coordinated military actions in the eastern part of the DR Congo.
Maj. Gen. Olum claimed that security forces had known for at least two days prior to Friday night's strike that rebels were in the border area on the Congolese side.
However, locals have complained that the government isn't ready for an assault.
One local told reporters, "I want the security to tell us where they were when these killers came to kill our people if they are telling us the borders are secure and security is tight."
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Last week, alleged ADF fighters attacked a community in the Democratic Republic of the Congo (DRC) near the Ugandan border, killing dozens of people there. More than a hundred people who had fled to Uganda are now back in their hometown.
This is the first time in 25 years that a school in Uganda has been attacked. The school was less than 2 kilometers (1.25 miles) from the Congolese border.
In a June 1998 attack on Kichwamba Technical Institute, located near the border with the Democratic Republic of the Congo, the ADF burned to death 80 students in their dormitories. There were kidnappings of over a hundred pupils.
Richard Moncrieff, an expert in the region at the International Crisis Group, has speculated that the group may target schools as a means of recruiting minors. But, he told the BBC, they do it for the sake of shock.
"These are terrorist groups who want to make an impact through violence, they want to show that they are there, show that they are active to their colleagues and allies in Isis in other parts of the world," Mr. Moncrieff added, using an alternative acronym for IS.
The ADF emerged in Uganda's east in the 1990s, and it has been fighting the government of long-time President Yoweri Museveni ever since over what it claims is its persecution of Muslims.
According to official government statistics, Muslims make up around 14% of Uganda's population, however the Ugandan Muslim Supreme Council puts that number closer to 35%
Muslims in Uganda report being discriminated against in a variety of settings, including schools and the workplace.
When the Ugandan army defeated them in 2001, the ADF fled to the Democratic Republic of the Congo's North Kivu province.
Jamil Makulu, the group's primary founder, was apprehended in Tanzania in 2015 and is currently being held in a prison in Uganda.
For over two decades, the ADF has launched attacks inside the Democratic Republic of the Congo.
It was not until April 2019 that IS admitted its involvement in the area, despite reports that Musa Seka Baluku, Makulu's successor, had pledged allegiance to the group as early as 2016.
Even though Islamic State as an organization has been mostly crushed, there are still many extremist groups in the Middle East and Africa that claim allegiance to IS.
The ADF was implicated for a slew of attacks, including suicide bombs in Kampala, late in 2021, despite having been dormant in Uganda for years.