Nigeria's military has again killed a large number of civilians with an airstrike it says was targeting militants instead, a mistake that has occurred a number of times in recent years and raises questions about the capabilities of a U.S. security partner. The latest such strike occurred on Sunday, when Amnesty International’s Nigeria office says at least 100 civilians — some of them children — were killed at a market in Tumfa town in northwestern Zamfara state. A Red Cross official in the state confirmed the airstrike to The Associated Press and said “multiple civilians” were killed. Nigeria ’s military, however, denied killing civilians. Maj. Gen. Michael Onoja confirmed an airstrike at the market but said there was “no verifiable evidence of civilian casualties," and said military operations continued in the area.…