A Queen's Guard pointed his rifle at a member of the public outside Buckingham Palace when an argument erupted with a police officer, it has emerged.
The soldier left his post to intervene when the man refused to stop shouting at the officer outside the palace gates on Friday.
A photograph published in The Sun on Sunday shows the guard pointing his bayonet-fixed rifle towards the man's face while stood next to the police officer.
A Metropolitan Police spokesman said: "Police were made aware of a disturbance at the North-Centre Gate of Buckingham Palace at approximately 5.50pm on Friday, April 4.
"Officers from Royalty Protection spoke to a man and he was given words of advice and there were no arrests."
The Queen's Guard is not believed to be facing any action over the incident.
An Army spokesman said: "We are aware of an incident outside Buckingham Palace on Friday and while no one came to any harm and there were no arrests, we are very clear that the Metropolitan Police lead on Royal Security arrangements including outside the Palace itself."
Buckingham Palace declined to comment.
The North-Centre Gate is now the everyday entrance to the Palace.
The Queen's Guard are a contingents of soldiers charged with guarding the Palace but carry a largely ceremonial role.
Earlier this year a man was jailed for 16 months after staging a stunt in which he jumped a vehicle barrier at the same Buckingham Palace entrance armed with a knife.
He was rugby tackled to the ground by armed police officers.
David Belmar, 44, said the incident in October was part of a protest against his Incapacity Benefit being stopped.