A Bangladesh Air Force jet crashed into a college in the capital Dhaka on Monday, killing at least 27 people, mostly children, according to officials, in the country’s deadliest air incident in recent memory.

The crash at Milestone School and College campus, in the Diabari neighborhood of northern Dhaka, injured 171 others, the Bangladesh Armed Forces said Monday. Most of the injured are students who are being treated in hospitals in the capital, the military said.

Students were attending afternoon classes when the BAF F7 jet hit the two-story campus around 1:18 p.m. local time (3:18 a.m. EST) after a mechanical fault, according to state media BSS News, citing the country’s armed forces.

The plane’s pilot made “every effort to divert the aircraft away from densely populated areas toward a more sparsely inhabited location,” the military said. The pilot was among those killed, The Associated Press reported, citing regional officials.

Authorities have launched an investigation into the cause of the crash.