U.S. President Barack Obama and other Americans paused Friday morning, remembering the children and adults gunned down by a 20-year-old in Newtown, Connecticut, one week ago.

Church bells rang in Newtown and other U.S. towns and cities as mourners stood in silence. Authorities say Adam Lanza killed his mother, then went to an elementary school, killing 20 children and six adults before taking his own life.

The attack at Sandy Hook Elementary was the second-worst school shooting in U.S. history.

The mass shooting has renewed the fierce debate on gun control and gun violence.

The country's largest gun lobby, the National Rifle Association , said Friday that tragedies like the Newtown massacre can be prevented by armed security, saying a protective security plan is needed in each school in America. The NRA news conference was disrupted several times by protesters who blame the group for gun violence.

After the attack, President Obama said action is needed to prevent such a tragedy in the future. Earlier this week, he called on Congress to reinstate an assault weapons ban that lapsed in 2004. The gunman in the Newtown attack used a military-style weapon.

Vice President Joe Biden is leading a government effort to find solutions to gun violence, including consulting with mental health and legal experts.

Families on Friday saying their final farewells to their loved ones, as the somber task of holding funerals for the victims continued.

The worst U.S. school shooting occurred in 2007, when a gunman opened fire at a Virginia university, killing 32 people before taking his own life.