The coronation of King Charles III involves one of the most important security operations in U.K. history, Britain’s security minister said Wednesday, after police arrested a man and blew up a suspicious bag outside Buckingham Palace.

The incident happened four days before scores of foreign royals, dignitaries and heads of state are expected to attend the coronation of King Charles III.

Security Minister Tom Tugendhat said the coronation involves “one of the most important security operations that the country has put into plan.”

“This is an enormously important moment for the country,” Tugendhat told Times Radio. “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.”

The Metropolitan Police said officers arrested a man on Tuesday evening after he approached the palace gates and threw items suspected to be shotgun cartridges into the palace grounds.

Police said the man was searched and a knife was found. He was arrested on suspicion of possession of an offensive weapon.

Video footage showed a man being walked backwards away from the palace gates by police officers.

A bag found with the suspect was deemed suspicious and blown up in a controlled explosion, the police force said. The force said no shots were fired and no one was injured.

Police said the incident was not being treated as terrorism-related.

Charles and Camilla, the queen consort, were not at Buckingham Palace at the time.

The incident took place just days ahead of Charles’ coronation ceremony, which is scheduled to take place at nearby Westminster Abbey. Buckingham Palace has seen a flurry of activity as tourists and international media begin to descend for the coronation — the first to take place in the country since Queen Elizabeth II was crowned in 1953.