"I was deeply saddened by Friday's senseless violence in Newtown, Connecticut," the pontiff told crowds of pilgrims gathered in St Peter's Square in Vatican City.
"I assure the families of the victims, especially those who lost a child, of my closeness in prayer. May the God of consolation touch their hearts and ease their pain."
"Upon those affected by this tragedy, and upon each of you, I invoke God's abundant blessings!"
On Friday a 20-year-old gunman identified as Adam Lanza forced his way into the Sandy Hook Elementary School in Newtown where he shot dead six adult women, and 12 girls and eight boys aged six and seven years old, before killing himself.
Services to mourn the victims have been held at St. Rose of Lima Catholic Church in Newtown.
(Reporting by Naomi O'Leary; Editing by Mark Heinrich)