As three more victims were to be buried, the head of the National Rifle Association blamed violence on the entertainment industry and called for federally funded armed police officers in every U.S. school.
Adam Lanza burst into Sandy Hook Elementary School last Friday and opened fire, killing 20 children and six adults before killing himself. He had killed his mother, Nancy, before going to the school.
"20 beautiful children & 6 remarkable adults. Together, we will carry on & make our country worthy of their memory. -bo," President Barack Obama tweeted. The president took part in the moment of silence before leaving the White House to attend the funeral of Sen. Daniel Inouye, D-Hawaii.
Bells at the National Cathedral and churches across the country, tolled 26 times to mark the 9:34 a.m. EST start of the massacre.
A short time later, Wayne LaPierre, executive director of the NRA, spoke to reporters and called for congressional funding to place armed police officers in every U.S. school. LaPierre took no questions from reporters in what had been billed as a news conference.
The NRA issued a public statement this week saying its members were "shocked, saddened and heartbroken" by the massacre but had otherwise kept a low profile since the shootings. Its Internet presence went dark soon after the massacre.
LaPierre said Friday the children at the Sandy Hook school were "utterly defenseless" against Lanza because there were no armed adults.
"Can't we afford to put a police officer in every single school?" he asked.
LaPierre's speech was interrupted twice by protesters. A man was escorted out when he tried to shout down LaPierre with anti-NRA remarks, and a woman who unfurled a banner and accused the organization of having "blood on its hands."
"Now, we must speak ... for the safety of our nation's children. Because for all the noise and anger directed at us over the past week, no one -- nobody -- has addressed the most important, pressing and immediate question we face: How do we protect our children right now, starting today, in a way that we know works?" LaPierre asked.
LaPierre criticized laws that ban guns around schools and blamed the violence on the entertainment industry, especially video games and movies.
"The only way to stop a monster from killing our kids is to be personally involved and invested in a plan of absolute protection. The only thing that stops a bad guy with a gun is a good guy with a gun," he said.
Three more victims of the Newtown massacre were to be buried Friday. Lanza's mother was interred Thursday while Lanza's burial plans have yet to be finalized, CNN said.
Obama again ordered flags to half-staff Friday.
The Obama administration began an effort Thursday to change U.S. gun laws. Vice President Joe Biden met with Cabinet members and law enforcement leaders at the White House to start developing what Obama called "real reforms right now."
More than 195,000 people signed an online White House petition in support of new gun control legislation.
In a letter published Thursday in The Hartford (Conn.) Courant, first lady Michelle Obama said Americans "have been united in our grief" at the events in Newtown.
She expressed admiration for "the first responders who risked their lives at a moment's notice; the educators whose devotion to their students shone brightest in one of our nation's darkest hours; the children who comforted each other despite their fear; the families coming together to support each other as they grieve."
The first lady expressed pride at the outpouring of support from across the country.
"[Please] know that every minute of every day, we are thinking of you, and praying for you, and holding you and your families in our hearts as you begin the slow and wrenching work of healing and moving forward," she said.