LONDON (AP) — British police say an officer assigned to the royal protection unit has been arrested after ammunition was found in personal lockers on the grounds of Buckingham Palace.

Police said Thursday the ammunition is thought to have come from Metropolitan Police supplies.

The officer is being questioned on suspicion of misconduct in public office and unlawful possession of ammunition. He has been suspended from duty.

Police said the officer usually works in a protection role but is not assigned to guard any individual members of the royal family. His home is being searched.

The arrest follows an investigation by the Directorate of Professional Standards.

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