The British police conducted a controlled explosion outside Buckingham Palace on Tuesday, detonating a bag taken from a man who they said had thrown suspected shotgun cartridges onto palace grounds just days ahead of King Charles III’s coronation.

There were no injuries and no shots were fired, but the man was swiftly detained and subsequently arrested after he was found to be carrying a knife, London’s Metropolitan Police said. He was not in possession of a firearm and the incident is not currently being treated as terror related, they added.

The man was detained after throwing items “suspected to be shotgun cartridges” and was found to be carrying “a suspicious bag,” the police said in a statement. The police said they conducted a controlled explosion on the bag “as a precaution” following an assessment by specialists who arrived on scene.

They did not say what made the bag suspicious, or whether it turned out to contain anything dangerous.

The episode came amid simmering tensions in the run-up to the event on Saturday when Charles will be formally crowned. The Metropolitan Police sent warning letters this week to anti-monarchists planning to protest at the coronation. New laws that will come into effect on Wednesday will give the authorities powers to swiftly arrest and search potential disrupters, and will carry the threat of stiff prison sentences.

The motives of the man responsible for the incident on Tuesday were not immediately clear. The BBC reported that the king and queen consort were not at the palace at the time, but the Metropolitan Police would not confirm this.

Metropolitan Police Chief Superintendent Joseph McDonald said that officers had “worked immediately to detain the man and he has been taken into police custody,” according to the statement. “Officers remain at the scene and further enquiries are ongoing.”