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(CNN) — A Secret Service officer on the south side of the White House complex observed a “quad copter” drone, approximately two feet in diameter, flying at a low altitude early Monday morning, a spokesperson for the department said, adding that the drone eventually crashed on the southeast side of the complex.

The crash triggered an immediate lockdown of the complex until the device was examined and cleared.

“An investigation is underway to determine the origin of this commercially available device, motive, and to identify suspects,” the spokesperson said.