Wiping away tears and pausing to collect his emotions during a nationally televised appearance, President Barack Obama mourned the "beautiful little kids between the ages of five and ten years old" who were killed at a school shooting in Connecticut.
"As a country we have been through this too many times," Mr Obama said, ticking off a list of recent shootings.
"We're going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics," Mr Obama said.
The comment was an apparent reference to the influence of the National Rifle Association over members of Congress.
Mr Obama expressed "overwhelming grief" as a parent, and said he deplored the "heinous" attack by a heavily armed gunman at a school that killed 26 people, including 20 children.
The shooter is also dead, police said.
Mr Obama remains committed to trying to renew a ban on assault weapons, White House spokesman Jay Carney said.
Latest shooting rampage
The United States has experienced a number of mass shooting rampages this year, most recently in Oregon, where a gunman opened fire at a shopping mall on Tuesday, killing two people and then himself.
The deadliest came in July at a midnight screening of a Batman film in Colorado that killed 12 people and wounded 58.
The Sandy Hook tragedy would be the deadliest elementary school shooting in US history.
The worst US high school shooting happened in 1999 when two students, Dylan Klebold and Eric Harris, went on a rampage at Columbine High School in Littleton, Colorado, killing 12 students and a teacher before turning their guns on themselves.
In 2007, 32 people were killed at Virginia Tech university in the deadliest act of gun violence in US history.
In another notorious school shooting outside of the United States, in 1996 a gunman opened fire in an elementary school in Dunblane, Scotland, and killed 16 children and an adult before killing himself.