A Queen's Guard pointed his bayonet-fixed rifle at a member of the public outside the gates of Buckingham Palace when an argument erupted with a police officer, The Sun on Sunday reported.
The soldier left his post to intervene when the man refused to stop shouting at the officer outside the palace gates on Friday, the paper reported, with a photograph showing the guard pointing his rifle towards the man's face.
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.