U.S. President Barack Obama has called on Congress to reinstate an assault weapons ban, five days after a gunman with a military-style weapon killed 20 children and six adults in the second-worst school shooting in the nation's history.

President Obama says he has named Vice President Joe Biden to lead an effort to come up with a set of concrete proposals addressing gun violence no later than January. He noted that a number of Americans, including police officers, have been killed by gun violence since Friday's deadly attack in Newtown, Connecticut.

He said questions remain after the school shooting.

“We may never know all the reasons why this tragedy happened. We do know that every day since more Americans have died of gun violence. We know such violence has terrible consequences for our society. And if there is even one thing that we can do to prevent any of these events, we have a deep obligation, all of us, to try.”

President Obama also called for background checks for people buying weapons from private dealers.

The president noted that funerals are continuing Wednesday for the victims of the Connecticut attack. Family, friends and loved ones are saying final farewells to the school's principal, a teacher and at least three more of the children.

Classes resumed at all Newtown schools Tuesday, except Sandy Hook. Officials say plans are under way to move classes to a school in the nearby town of Monroe, possibly in January.

Also, investigators are trying to determine a motive. Authorities believe 20-year-old Adam Lanza killed his mother at home and then took some of her guns with him to the school.

The deadly rampage has re-ignited the gun control debate in the United States.

California Democratic Senator Dianne Feinstein, the author of the assault weapons ban that lapsed in 2004, said she would introduce new legislation at the start of the next Congress in January.

The worst U.S. school shooting occurred in 2007, when a gunman killed 32 people at the Virginia Polytechnic Institute and State University, known widely as Virginia Tech.