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The scene outside the General Santander police academy is chaotic, with ambulances and helicopters rushing to the normally tightly controlled facility.
Witnesses say they heard a loud explosion that destroyed windows in adjacent buildings Thursday.
Pictures on social media showed a charred vehicle surrounded by debris on the academy's campus.
Mayor Enrique Penalosa says at least 5 people were killed and 10 injured.
Leftist rebels from the National Liberation Army have been stepping up attacks on police targets in Colombia amid a standoff with conservative President Ivan Duque over how to re-start stalled peace talks.