ABUJA (Reuters) - Nigeria s President Muhammadu Buhari appealed for calm and an end to communal violence on Saturday after police said armed herdsmen killed 19 people in the central state of Plateau.  Local police said Fulani herdsmen attacked Ancha village, in the Bassa local government area of Plateau state, in the early hours of Friday. They said it was thought to be a reprisal attack after a boy from the herding community was killed.  Police provided details of the attack, in which five people were injured, late on Friday.  Fighting between semi-nomadic cattle herders and more settled communities over land use claims hundreds of lives a year in Nigeria s central and northern states.   I urge all our communities in the state and the other parts of the country to embrace peace and bring to a stop these painful and unnecessary killings,  said Buhari, in an emailed statement. He said communities and security agencies in Plateau had taken steps to  pull the state back from the brink of anarchy and senseless killings , adding that it would be  a painful loss to allow these unsavory acts to return . The violence is another security challenge for Buhari in addition to the eight-year Boko Haram jihadist insurgency in the northeast and attempts to maintain a fragile ceasefire in the southern Niger Delta energy hub where militant attacks on oil facilities last year cut crude production by more than a third. 