Wayne LaPierre spoke to reporters in an appearance that was interrupted twice by protesters shouting anti-NRA slogans and bearing banners in front of his podium, including one that said, "NRA killing our kids."
The nation's most prominent gun rights lobby joins "the nation in horror, outrage and earnest prayer for the families" who "suffered such an incomprehensible loss" in Newtown, Connecticut, LaPierre said.
However, he said, schools remain a target by criminal gunmen because they are not protected by armed security the way other important institutions are.
Policies banning guns at schools create a place that "insane killers" consider "the safest place to inflict maximum mayhem with minimum risk," LaPierre said.
Such policies leave schoolchildren "utterly defenseless, and the monsters and the predators of the world know it," he said.
Friday's event was billed as a news conference, but LaPierre only read a statement; he took no questions.
One week ago, a gunman forced his way into Sandy Hook Elementary School and shot 20 students, six adults then himself dead in Newtown.
Adam Lanza had killed his mother before arriving at the school.
Across the nation Friday morning, church bells rang in remembrance of the victims. The NRA was among those groups that observed a moment of silence at 9:30 a.m., the same time as last week's massacre.
Despite the relative silence early on from the powerful lobbying group's offices in Fairfax, Virginia, the NRA is regrouping in anticipation of a massive legislative push for gun control legislation, a gun policy expert said.
Kristin Goss, an associate professor of public policy and political science at Duke University and author of "Disarmed: The Missing Movement for Gun Control in America," said that strategy is part of the organization's playbook after an incident such as this one.
After such a terrifying event, when there is a national outcry, the NRA typically lays low, Goss said.
"They're used to seeing this cycle, express condolences and hope the attention will shift to a new issue."
Obama starts gun control debate
This week, the Obama administration put into motion an effort to change U.S. gun laws.
Vice President Joe Biden met with Cabinet members and law enforcement leaders at the White House to start formulating what Obama called "real reforms right now."
More than 195,000 people have signed an online White House petition supporting new gun control legislation.
A slight majority of Americans favor major restrictions on guns: 52%, up five points from a survey taken in August after the July shooting inside a movie theater in Aurora, Colorado, where 12 people died, according to a CNN/ORC International poll released Wednesday.
Biden will lead a White House effort to craft proposals aimed at preventing another tragedy such as the Newtown shootings. The recommendations are due sometime in January.
That same month, several lawmakers have promised to introduce or reintroduce gun control legislation, ranging from a reinstatement of a federal ban on assault weapons to banning the sale of high-capacity magazines.
Since the shootings, a number of conservative Democrats and some Republicans who have supported gun rights have said they are open to discussing the issue.
Sen. Dianne Feinstein, D-California, said she will introduce legislation to reinstate the assault weapons ban that expired in 2004. The White House has said that the president supports that effort.
House Democratic Leader Nancy Pelosi took her own step towards reform Wednesday by announcing a new task force on preventing gun violence.
Pelosi said the task force will work towards restoring the assault weapons ban, strengthening the background check system, and addressing mental health and violence issues.
The NRA, with its roughly 4.3 million members, is the standard-bearer for protecting the Second Amendment. It is also the source of hefty campaign donations.
During the 2012 election cycle, the NRA donated $719,596 to candidates. Republicans received $634,146 of that, according to the Center for Responsive Politics' analysis of federal campaign data.
Some $85,450 went to Democrats, many of them in states that are considered more conservative when it comes to gun control laws.
Tributes ongoing for victims
Carloads of teenagers from a Minnesota school that suffered a mass shooting in 2005 headed toward Newtown on Thursday to offer their support.
Also Thursday, burials were held for three children and two teachers.
More than 2,200 miles west of Newtown, Ogden, Utah, the hometown of shooting victim Emilie Parker, was festooned with pink ribbons as her parents brought her body back for burial.
"This sucks -- there's no reason for us to be here tonight," her father, Robbie Parker, told friends and well-wishers at a memorial service Thursday night. "And I'm so thankful for everybody that's here."
His voice trailed off as he struggled for composure. Seeing the pink -- his slain daughter's favorite color -- made him and his wife, Alissa, "feel like we were getting a big hug from everybody."
Also buried Thursday, at an undisclosed location, was Nancy Lanza, the shooter's mother, whom he killed before the school rampage, said Donald Briggs, a friend of the family who grew up with her in Kingston, New Hampshire.
Plans had not been finalized for the burial of the gunman, her son, Adam.
Three 6-year-olds were among those buried Thursday: Allison Wyatt, who loved to draw and wanted to be an artist; Benjamin Wheeler, who loved the Beatles; and red-haired Catherine Hubbard, who loved animals.