Italians have reacted with indignation to two tourists who stripped down to their underwear and cavorted in a fountain in Rome beneath a monument that commemorates the dead of the First World War.

One of the young men pulled down his underpants to reveal his genitals, in a scene that was captured on video by a passerby.

As the capital sweats through the dog days of August, it is not common for international visitors to try to cool off in the city’s many Baroque and Renaissance fountains, despite signs warning that it is prohibited.

But the latest episode provoked particular anger because the fountain that the two men clambered into is part of the Altar of the Fatherland, a giant white stone monument in the centre of Rome that includes the Tomb of the Unknown Soldier and an eternal flame.

“I condemn in the strongest terms this behaviour, which offends each one of us, as well as the memory of those who died for our country, to whom the monument is dedicated,” said Luca Bergamo, the deputy mayor of Rome.