DAKAR (Reuters) - The United Nations on Thursday called for an investigation after Reuters reported that Cameroonian soldiers opened fire on fleeing civilians during a weekend raid, killing up to nine people. Three witnesses told Reuters that soldiers entered the village of Mautu in the South West region - at the heart of a separatist insurgency - raided homes and shot civilians as they ran for cover under nearby cocoa bushes. The Cameroonian military denies wrongdoing. It said it was conducting a raid on separatist positions when it came under fire and had killed what it labelled “terrorists”. “Deeply concerned & saddened by the attack on Mautu ... that claimed the lives of many civilians. I call for an investigation into this attack,” said the head of the U.N.’s Central Africa office, François Louncény Fall, on Twitter. Britain also expressed concern. “There must be an urgent and impartial investigation, and the perpetrators must be brought to justice,” the British High Commission in Yaounde said on Twitter. For four years the army has clashed with Anglophone separatist fighters among the forests and cocoa farms of western Cameroon. Over 3,000 people have died in the violence, which has intensified since the start of this year. The witnesses said they saw nine dead people, including a child and an old woman. None of the dead was a separatist fighter, they said. Medical charity Medecins Sans Frontieres (MSF) said it was treating four people from the village, all with gunshot wounds: a young child, two elderly patients and a young woman. International players have long called for peace. Abuses on both sides have made talks difficult. Sunday’s attack comes as three soldiers face trial for their alleged involvement in the killing of 21 civilians last year in a village in the North West region.