A lieutenant said no one let Adam Lanza, identified by police as the shooter, into the Newtown school. Authorities further retraced the 20-year-old's steps, saying he shot his mother and then drove to Sandy Hook Elementary School. He killed 20 children, six adults, including the principal and a school psychologist, and himself.

"We grieve for the families of those we lost," Obama said. "And we keep in our prayers the parents of those who survived."

Obama also demanded "action to prevent more tragedies like this." However, he went no further than that, stopping short of specifically calling for tighter gun-control laws.

'All the rhetoric'

New York City Mayor Michael Bloomberg, who runs a coalition of mayors on gun policy, said on Friday that the president should press ahead despite likely opposition from the Republicans who control the US House of Representatives.

"We have heard all the rhetoric before," Bloomberg said in a statement. "What we have not seen is leadership - not from the White House and not from Congress. That must end today."

The partisanship enhanced by the looming "fiscal cliff" of tax hikes and spending cuts, has been otherwise set aside, though. House Speaker John Boehner canceled the Republican weekly address for Saturday "so that President Obama can speak for the entire nation at this time of mourning."

"We have endured far too many of these tragedies in the last few years," Obama said at a White House address Friday. "This weekend, Michelle and I are doing what I know every parent is doing: holding our children as close as we can and reminding them how much we love them. There are families in Connecticut who can't do that today. And they need all of us now. All of us can extend a hand to those in need - to remind them that we are there for them, that we are praying for them."

Obama recalled a shopping-mall shooting that took place on Tuesday in Oregon, as well the July massacre at a Colorado cinema and August's hate attack at a Sikh temple in Wisconsin.

"As a country, we have been through this too many times," Obama said. "Most of those who died were just young children with their whole lives ahead of them," he added. "And every parent in America has a heart heavy with hurt."

Words from abroad

Following the shooting, condolences from America's allies began pouring in.

"The news from Newtown makes me deeply sad," German Chancellor Angela Merkel said. "We are confronted once again with a crime that we cannot make sense of."

"My deep sympathy goes out to the relatives," she added. "I wish them strength and care. I hope they do not remain alone in their pain."

"I was shocked and deeply saddened to hear about today's horrific shooting," British Prime Minister David Cameron said in a statement. "My thoughts are with the injured and those who have lost loved ones. It is heartbreaking to think of those who have had their children robbed from them at such a young age, when they had so much life ahead of them."

France's President Francois Hollande expressed "deep shock and consternation."

UN Secretary General Ban Ki-moon sent a condolence message to Connecticut Governor Dan Malloy. "The targeting of children is heinous and unthinkable," he said

Pope Benedict XVI called the killing a "senseless tragedy" and conveyed his "heartfelt grief."

mkg/dr (AFP, Reuters, dpa, AP)