A 38-year-old man was arrested on suspicion of possessing a firearm, namely a Taser, outside the Buckingham Palace. Police were called at 12:47 local time on Sunday to the visitors' entrance after the man was detained by security staff.
The man was taken into custody at a central London police station and remains there, according to the police report.
There's no comment from Buckingham Palace so far.
The Royal family is currently elsewhere.
While owning a taser is legal for personal self-defense in the US, the stun guns, which are capable of discharging an electrical current, are classified as prohibited firearms in the UK.