Two Mexican military officers died in a plane crash in the western state of Baja California Sur, the Navy Secretariat said.

Wednesday’s accident occurred 34 kilometers (21 miles) southwest of the state capital of La Paz for unknown reasons, resulting in the death of an air force major and a navy lieutenant commander.

The two-seat, single-engine Zlin 242-L was part of the fleet of the La Paz-based Naval Aviation School.

The Czech-made aircraft was being used for training purposes when an emergency alarm was activated and the plane fell from the sky, the secretariat said in a statement.

“An investigation has been launched to determine what may have caused the accident,” the statement said.