London, UK - A man is being questioned by British police after suspected shotgun cartridges were thrown into the grounds of Buckingham Palace, days before King Charles III's coronation.

The suspect was detained at about 7 PM local time on Tuesday after he approached the palace's gates in central London and threw a number of items, the Metropolitan Police said.

He is being held on suspicion of possession of an offensive weapon after a knife was found, the force said.

Police carried out a controlled explosion while cordons were put up in the area.

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Scotland Yard say they are not treating the incident as terror-related.

It is understood it is being treated as an isolated mental health incident.

The arrest comes as a ring of steel is expected in the capital for King Charles III's coronation at Westminster Abbey on Saturday.

Neither the king nor queen consort Camilla Parker Bowles were at Buckingham Palace at the time of the incident.

The items thrown into the palace grounds "have been recovered and will be taken for specialist examination," the Met Police said.

The man was also found with a "suspicious bag," the force added.