Israeli troops killed three Egyptian policemen mistaken for Palestinian militants along the Gaza-Egypt border early Thursday, in what the army called a “professional and operational” mishap. Israel immediately apologized and opened an investigation into the incident, which threatens to increase tensions between the two countries. The former enemies signed a peace agreement in 1979 but often have had shaky relations. The timing of the incident is especially sensitive because Israel wants Egypt to help secure the Gaza Strip after Israel’s planned withdrawal next year from the coastal area. Full Story