US President Joe Biden has vowed to act on the country's gun laws after mass shooting at an elementary school in Texas that killed 19 children and two adults.
Speaking at the White House, Mr Biden said the massacre at Robb Elementary School in Uvalde proved that now was "time to turn this pain into action".
"As a nation we have to ask, when in God's name are we going to stand up to the gun lobby?" he said.
"When in God's name — what we all know we need to do in our gut — do what needs to be done?
"I am sick and tired of it. We have to act. Don't tell me we can't have an impact on this carnage."
Mr Biden became emotional as he spoke of past mass shootings at schools, including Sandy Hook in 2012.
"It's been 3,448 days, 10 years, since I stood up at a grade school in Connecticut, where another gunman massacred 26 people, including 20 first-graders, at Sandy Hook Elementary School," he said.
"Since then, there's been over 900 incidents of gunfire reported on school grounds.
"Marjorie Stoneman, Santa Fe, Oxford High School in Michigan ... the list goes on and on and grows when you include mass shootings at movie theatres, houses of worship, and as we saw 10 days ago at a grocery store in Buffalo, New York."
Mr Biden said he learnt of the shooting while returning to the US from Tuesday's Quad meeting in Tokyo, Japan.
"What struck me on that 17-hour flight ... was these kinds of mass shootings rarely happen anywhere else in the world. Why?" he said.
"They have mental health problems. They have domestic disputes in other countries. They have people who are lost, but these kinds of mass shootings never happen with the kind of frequency they happen in America — why? Why are we willing to live with this carnage? Why do we keep letting this happen?
"Where in God's name is our backbone to have the courage to deal with it and stand up to the lobbyists?
'Common sense' laws have positive impact, Biden says
Mr Biden said most Americans were supportive of what he described as "common-sense gun laws" that had reduced the number of mass shootings in years gone by.
"I spent my career as a senator and a vice-president working to pass common-sense gun laws. We won't prevent every tragedy, but we know they work and have positive impact," he said.
"When we passed the assault weapons ban, mass shootings went down. When the law expired, mass shootings tripled.
"The gun manufacturers have spent two decades aggressively marketing assault weapons which make them the most and largest profit. For God's sake, we have to have the courage to stand up to the industry."
Mr Biden said he had hoped he would never have to make an address about another shooting as President, and paid tribute to the "beautiful, innocent, second, third and fourth graders" who were killed.
"How many scores of little children who witnessed what happened, see their friends die, as if they're in a battlefield, for God's sake?" he said.
Mr Biden also offered his condolences and prayers to those parents "who will never see their child again".
"Never have them jump in bed and cuddle with them. Parents who will never be the same," he said.
"To lose a child is like having a piece of your soul ripped away. There's a hollowness in your chest. You feel like you're being sucked into it and you're never going to be able to get out. Suffocating. It's never quite the same.
"Our prayer tonight is for those parents.They're lying in bed trying to figure out, 'Will I be able to sleep again? What do I say to my other children? What happens tomorrow?'
"May the Lord be near the broken-hearted and save those crushed in spirit. They're going to need a lot of help — a lot of our prayers."
Earlier, US Vice-President Kamala Harris said America needed to "take a stand" after the shooting.
"I would normally say in a moment like this, we would all say naturally that our hearts break, but our hearts keep getting broken," she said.
"Enough is enough. As a nation, we have to have the courage to take action and understand the nexus between what makes for reasonable and sensible public policy to ensure something like this never happens again.
"I know this is a room full of American leaders who know and have the courage to take a stand. And so let us tonight, as we do every time we all get together, recommit ourselves to having the courage to take action."
