A controlled explosion was performed outside Buckingham Palace on Tuesday after a man was arrested on suspicion of possessing a weapon, the Metropolitan Police said.
He was held at about 7pm after he approached the gates and threw several items, including what was believed to be shotgun cartridges, on to palace grounds.
Deputy Assistant Commissioner Ade Adelekan said the man had approached officers asking to see a soldier at about 7.15pm on Tuesday.
When the officers said that was not possible, the man allegedly began throwing shotgun cartridges over the gates of Buckingham Palace.
He was searched and allegedly found to be in possession of a lock knife, and was arrested on suspicion of possession of a knife and ammunition.
During the arrest, the man told officers that they should handle his rucksack with care, which led to a controlled explosion being carried out on the bag.
Mr Adelekan said the suspect was detained within seconds and arrested within five minutes.
He said he had no knowledge of reports that the man had been shouting that he wanted to kill the king before he was arrested.
The suspect has undergone a mental health assessment and has been deemed fit to be interviewed, police said on Wednesday.
Neither King Charles nor Queen Consort Camilla were at Buckingham Palace at the time of the arrest.
But the monarch had hosted Australian Prime Minister Anthony Albanese during an audience at the palace earlier on Tuesday.
The royal residence was cordoned off after the incident.
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It is understood the incident is being treated as an isolated mental health event, not related to terrorism.
“Officers worked immediately to detain the man and he has been taken into police custody,” Chief Superintendent Joseph McDonald said on Tuesday.
“There have been no reports of any shots fired, or any injuries to officers or members of the public.
“Officers remain at the scene and further inquiries are ongoing.”
Buckingham Palace declined to comment and said the incident was a matter for the Metropolitan Police.
Home Office minister Tom Tugendhat told Times Radio on Wednesday: "The police are, to put it mildly, all over it and our intelligence and other security forces are extremely aware of the challenges that we face and ready to deal with them – as the police did quite brilliantly yesterday."
A ring of steel is expected in the capital for King Charles’s coronation at Westminster Abbey on Saturday, as hundreds of thousands of people descend on the capital for the event.
Policing minister Chris Philp has described it as a “huge policing operation”, and heads of state and foreign royals from around the world are expected to travel to the UK.
Mr Tugendhat added: “What we’ve been planning for a number of months now is one of the most important security operations that the country has put into plan.
“The reason for that is this coronation is not just an opportunity to celebrate our new King, but also an opportunity to showcase the United Kingdom to the world.
“So we’re very conscious that there are going to be quite literally thousands, possibly hundreds of thousands of foreign tourists, there are going to be many film crews and journalists from around the world and of course, we’re going to have heads of state and government coming to celebrate with us on Saturday."
