Scuffles broke out between security staff and peace activists at Milan Cathedral.
In a video on the online portal "Il Fatto Quotidiano" (Monday), the activists can be seen holding up banners in front of the altar during a church service and calling for a global ceasefire.
"We want peace on earth. No more war," shouts one activist. "That's what the Pope says too. He says stop the armed violence," shouts another.
The video also shows security forces taking the banners away from the demonstrators, who try to prevent this.
This leads to a brief scuffle.
In Italy, peace and environmental activists repeatedly present their demands during church services.
In January, two animal rights activists interrupted a mass with Pope Francis in Rome.
During vespers in the Basilica of St Paul Outside the Walls, they demanded that the church should not bless bullfights.
After a few moments, they were led out by security forces.