Mayhem struck at an elementary school in the northeastern state of Connecticut after a gunman opened fire and killed 26 people - most of them young children.
The mass shooting took place Friday morning at Sandy Hook Elementary School in Newtown, Connecticut, a small town 130 kilometers northeast of New York City.
Connecticut State Police Lieutenant J. Paul Vance told reporters the fatalities included students and staff, and that the gunman involved also was dead. By mid-afternoon, a police spokesman told reporters the crime scene had been secured. He said the first emergency call came shortly after 9:30 a.m. Police descended on the scene and immediately entered the school. Eighteen of the children and six adults, including the shooter, were found dead in one section of the school in two separate rooms. Two other children died in area hospitals.
Mass killings, like Friday's schoolhouse slaughter in Connecticut, have become a troubling and recurring fact of life in the United States.
Other recent mass shootings include:
* August 2012: An Army veteran kills five men and a woman at a Sikh temple in Wisconsin.
* July 2012: A student opens fire at a midnight showing of the latest Batman movie at a Colorado theater, killing 12.
* January 2011: U.S. Representative Gabrielle Giffords and 18 other people are shot outside a supermarket in Arizona.
* November 2009: An Army psychiatrist kills 13 soldiers and civilians on the Fort Hood Army base in Texas.
* April 2007: A students kills 32 people on the campus of a large university, Virginia Tech.
* April 1999: Two students at a Colorado high school kill 12 classmates and a teacher.
The Mother Jones magazine says that since 1982, there have been at least 61 mass murders in the U.S., which U.S. authorities define as an assault in which a gunman kills four or more people, typically in a single location.
It is widely reported that the 20-year-old suspect's mother - a teacher at the school - was among the dead. Circumstances of her death remained unclear hours after the tragedy. The gunman's 24-year-old brother was undergoing police questioning late Friday.
An official from the governor's office says Governor Dannel Malloy was "horrified" by the tragedy and rushed to meet with the children's family members.
Photos and video images from the scene showed children being rushed out of the school, but it took several hours before the full scope of the tragedy to become known.
When it did, reports of heroism surfaced as well. In one widely reported instance, a teacher herded her entire first grade class into a bathroom, locked the door, and cowered alongside the children until help arrived.
Tearful Obama calls for action
President Barack Obama called authorities in Connecticut to express his sadness, and pledged to help with federal resources. The White House said Obama spoke with the FBI director about the case, and received frequent briefings.
President Barack Obama wipes his eye as he speaks about the elementary school shooting in Newtown, Connecticut, Friday, Dec. 14, 2012, in the briefing room of the White House.
A tearful president expressed ``overwhelming grief'' for the victims of the shooting rampage and called on Americans to set aside politics and ``take meaningful action'' to prevent more tragedies of this kind.
``Our hearts are broken today,'' Obama said, his voice breaking at times during a nationally televised appearance in the White House briefing room.