The black soldier, who is not being named to protect him from further assaults, stuck to his training and did not retaliate. His restraint won praise from his commanding officer, Colonel Mark Ridley of the Blues and Royals.
'His regiment are outraged at this cowardly and unprovoked attack,' he said.
'As all soldiers are armed on duty, the trooper is to be commended for his self-control in not retaliating.'
The soldier was in full uniform outside Horse Guards Parade on Whitehall when he was attacked.
Three white youths sprayed a 'noxious substance' into his face before running off at around 1pm. The guardsman, a private in his early twenties, was treated by Army medical staff at Knightsbridge Barracks before returning to complete his watch.
Police yesterday appealed to tourists who were at the scene for help with their inquiries. Visitors expressed their 'disgust' at the attack.
Alam Khan, visiting family here with his wife and children, said: 'It is disgusting that a soldier doing his duty could be attacked in front of people, especially if he was chosen because of his skin.'
Brigadier Sebastian Roberts of the Ministry of Defence said the soldiers are given clear instructions about what kind of circumstances they may 'take action'.
'They can give a warning that they are armed and if the person does not desist then they may retaliate. It is commendable that he showed such forbearance.'
He added that it was not the first time a soldier has been targeted: 'Members of the public have attacked guardsmen before at St James' Palace and at Windsor, but on average, this happens once every two years. There have been prosecutions before and the police are working hard on this one.'
Detective Inspector Glenn Gavin, of Westminster Community Safety Unit, said: 'We are taking the attack very seriously and will appeal for witnesses, particularly from the tourists who would have been in the area at the time.'
The three attackers are all described as white and in their late teens. One was about 6ft 1ins tall with dark hair and wearing a yellow T-shirt. There was no description of the other two attackers.
