The Metropolitan Police said Monday the suspect didn't have any weapons on him and "the incident is not being treated as terrorist related."
He was arrested on suspicion of trespass and suspicion of possessing a controlled substance.
The department said its Royalty and Specialist Protection Command arrested the man after he allegedly stepped over a low fence and tried to scale a wall outside the palace.
Buckingham Palace is the official home of Britain's Queen Elizabeth II, although she is often at one of her other residences.
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