A joint operation by the United States and Nigeria against Islamic State fighters has killed 175 over the past few days, Nigeria’s military said on Tuesday, while the head of the US Africa Command said it showed the capabilities its forces could bring in Africa, home to the “epicentre of global terrorism”. The US sent troops to Nigeria in February in what was deemed a mostly advisory and training role, but the joint operation signals more active involvement. The US Africa Command, or AFRICOM,...