US President Barack Obama and first lady Michelle observed a minute of silence on the first anniversary of the Sandy Hook school shooting on Saturday.
The Obamas lit 26 candles for the 20 children and six school workers who died in Newtown, Connecticut, when a gunman opened fire last December.
"We have to do more to keep dangerous people from getting their hands on a gun so easily," said the president. "We have to do more to heal troubled minds. We have to do everything we can to protect our children from harm and make them feel loved, and valued, and cared for."
Gunman Adam Lanza killed his mother inside their Newtown home on December 14, 2012, before driving to Sandy Hook elementary school, where he carried out his rampage. The children he killed were all aged six and seven years old.
The 20-year-old killed himself as police arrived.
Newtown officials asked for quiet and privacy on the anniversary.
After the Newtown tragedy, Connecticut passed several new gun control and mental health measures, but a similar nationwide effort pushed by President Obama failed in the US Senate.
In Virginia, anti-gun violence protesters gathered outside the headquarters of the National Rifle Association, a day after another school shooting, this time at a Colorado high school where one student was wounded.
The group Mayors Against Illegal Guns says there have been 28 school shootings since Newtown.