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 at the White House 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.
Inaction in Washington
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.
The group Mayors Against Illegal Guns says there have been 28 school shootings since Newtown.
Anti-gun violence campaigners gathered in front of the National Rifle Association (NRA) headquarters in Virginia to mark the first anniversary of the school shooting.
A divided Congress denied President Barack Obama's calls for changes and the national gun lobby, led by the NRA, is arguably stronger than ever.
"Congress has failed to enact any sensible reform to our nation's lax gun laws " said Martina Leinz, president of the Northern Virginia Chapter of Million Mom March, the grassroots arm of the Brady Campaign to Prevent Gun Violence.
"There is one simple reason for this and it's the organisation behind me, right here, the National Rifle Association," she added.
The inaction in Washington underscores the ongoing potency of the NRA and other gun rights groups in Congress where Republicans oppose stricter gun laws and many Democrats are reluctant to anger voters.
"I believe that the shooting at Newtown was a paradigm shift in the American conscience," Leinz added.