Sixty-six children have been killed in Uganda's northeastern Karamoja region during military operations against armed pastoralists, according to a British charity.

The children died during a clash on 12 February in the remote district of Kotido, Save the Children (UK) said on Friday. "Save the Children has met 256 people in three locations who reported that the children were shot, crushed by armoured vehicles or killed by animals during raids by the army on a cattle ranch where they were living," it said in a statement.

The Ugandan military denied the charge, calling the report "[as] shocking as it is malicious". Army spokesman Maj Felix Kulaigye said the army was more interested in protecting lives and there could be no way they would kill children.

"Today I had a meeting with the defence minister who wanted to discuss with me the report and during our discussion they confirmed that there were clashes on that day, but could not confirm whether children were killed," Valter Tinderholt, the Save the Children country director in Uganda, told IRIN.

Reports of children being killed in an indiscriminate, illegal and inhumane way are absolutely devastating "They have agreed to institute an investigation to find out what took place," he added.

The charity said interviewees had reported that landmines were subsequently laid, creating ongoing risks for children. "Reports of children being killed in an indiscriminate, illegal and inhumane way are absolutely devastating," Tinderholt said. "Such allegations must be fully investigated and those involved brought to account."

The army insisted it had not used landmines since they were outlawed in Uganda years ago. "That report is terribly outrageous. It is shocking for us in the military that someone has the audacity to write such [things]. We did not trample over children," Kulaigye said.

The charity called for an independent investigation into the events and the prosecution of those found to be guilty or complicit in "these grave abuses against children".

The UN Children’s Agency (UNICEF) in Uganda expressed grave concerns over the report, and with the UN Office for the Coordination of Humanitarian Affairs (OCHA), the UN Human Rights Commissioner and other agencies, was verifying the allegations.

"We express serious concern about the impact of the escalating insecurity on the lives of children and families in Karamoja. Local and international agencies should undertake all measures required to protect vulnerable members of the society in Karamoja," UNICEF spokesman in Kampala, Chulho Hyun, said.

Karamoja region is Uganda’s ‘wild west’, where armed pastoralists raid each other for livestock in bloody skirmishes fuelled by the high proliferation of firearms; these clashes have left hundreds dead.

Efforts by government to disarm the tribesmen have yielded few results and the military operation to forcefully disarm the warriors has attracted criticism for heavy-handedness.