As the funerals begin in the Connecticut town where 26 died in an elementary school massacre, Barack Obama pledges to use "whatever power" he has to prevent further such shootings.
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The first funerals are planned for six-year-old Jack Pinto and Noah Pozner, who had his birthday two weeks ago. They will be buried a day after the community of Newtown came together for a vigil attended by the US president.
Mr Obama said he had come to Newtown to offer "the love and prayers of a nation" following the shooting on Friday at Sandy Hook elementary which saw the deaths of six staff and 20 children aged six and seven.
The president told Connecticut Governor Dannel Malloy that Friday was the most difficult day of his presidency.
In a speech in which he touched on the joys and anxieties of parenthood, Mr Obama spoke about the need to keep children safe. "If we don't get that right, we don't do anything right," he said.
"Can we say that we're truly doing enough to give all the children of this country the chance they deserve to live out their lives in happiness and with purpose?
"I've been reflecting on this the last few days," the president said. "And if we're honest with ourselves, the answer is no. We're not doing enough and we will have to change."
'Price of our freedom'
The president noted that this was the fourth time in his presidency when the nation had to come together in response to mass shootings. "We can't tolerate this any more," he insisted.
He signalled that he would at least attempt to take on the explosive issue of gun control.
"Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard? Are we prepared to say that such violence visited on our children year after year after year is somehow the price of our freedom?"
He made clear that the deaths compelled the United States to act, and that he was the leader of a nation that was failing to keep its children safe. He spoke of a broader effort, never outlining exactly what he would push for, but expressed outrage by yet another shooting rampage.
We're not doing enough and we will have to change US President Barack Obama
"Surely we can do better than this," he asked. "We have an obligation to try."
The president promised in the coming weeks to talk with law enforcement, mental health professionals, parents and educators on an effort to prevent mass shootings.
The shootings have restarted a debate in Washington about what politicians can to do help - gun control or otherwise. Mr Obama has called for "meaningful action" to prevent killings.
Democratic lawmakers said Sunday that military-style assault weapons should be banned and that a national commission should be established to examine mass shootings in the US.
Mr Obama and senate Democrats have not pushed for new gun controls since 2008, in the face of opposition from the National Rifle Association.
But gun control advocates also say the latest shooting is a tipping point that could change the dynamic of the debate.
Near the start of his remarks, Mr Obama read the names of the adults who died. He finished by reading the first names of the kids, slowly, in the most wrenching moment of the night. "God has called them home," he told the audience. Cries and sobs filled the room.
Police have said the 20-year-old gunman, Adam Lanza, was carrying an arsenal of ammunition big enough to kill just about every student in the school if given enough time. He shot himself in the head just as he heard police drawing near, authorities said.
A Connecticut official said the gunman's mother was found dead in her pyjamas in bed, shot four times in the head with a .22-calibre rifle. The killer then went to the school with guns he took from his mother and began blasting his way through the building.
Investigators have offered no motive for the shooting.