President Barack Obama has embraced grief-stricken families of young children massacred in their school, as demands increase for action on gun control.
A lone gunman killed 20 children, aged six or seven and six adults at Sandy Hook School in Newtown, Connecticut, on Friday.
Mr Obama spent several hours privately consoling relatives of the victims, and the first people to respond to calls for help.
Earlier, officials formally identified Adam Lanza, 20, as the shooter.
They also confirmed Lanza shot his mother several times in the head at the house they shared before going to his old school.
Mr Obama will speak at an interfaith vigil at Newtown High School at 7pm local time on Sunday.
Despite rain and cold conditions, queues stretch for at least 200 metres outside the auditorium.
Scores of people have left tributes at a memorial outside Sandy Hook School, while a minute's silence is being held before National Football League games across the United States on Sunday.
Before the president's visit, a service at St Rose of Lima Catholic Church was abandoned and the church was evacuated because of an unspecified threat, thought to have been a hoax called in by telephone.
Earlier Pope Benedict XVI paid tribute to the dead and their families in his weekly address at the Vatican, saying he was "deeply saddened".
Newtown is about 130km from New York City.
Children won't return
The BBC reports Sandy Hook School is unlikely to re-open.
Police say that children are unlikely to return to the classrooms where the shootings took place.
Surviving pupils will be taught at other schools in the area while a final decision about Sandy Hook's future is made.