BOGOTA, Colombia (AP) — At least four police officers were killed and another 42 injured when a homemade bomb exploded early Saturday outside a police station in the Colombian city of Barranquilla hours after a high-powered car bomb gutted another police station near the border in neighboring Ecuador. The two attacks didn't appear to be related, but they underscore the security challenges that have emerged since a 2016 peace deal with the Revolutionary Armed Forces of Colombia, which long played a dominant role in South America's drug trade. The blast in Barranquilla, redolent of some of the worst violence at the apex of Colombia's drug violence three decades ago, took place shortly after 6:30 a.m. local time as officers were lining up in formation at the police station's patio following a shift change.