WASHINGTON (Reuters) - President Barack Obama urged Americans on Friday to keep up the pressure on lawmakers to tighten gun regulations as a result of the mass shooting of 26 people in Newtown, Connecticut, a week ago.

Obama issued a videotaped response to the several hundred thousand people who have signed a petition posted on the White House website calling for toughened gun laws in response to the shooting, in which 20 school children and six adults were killed at a Newtown school.

"I need your help," Obama said in the video. "If we're going to succeed, it's going to take a sustained effort from mothers and fathers, daughters and sons, law enforcement and responsible gun owners, organizing, speaking up, calling their members of Congress as many times as it takes, standing up and saying 'Enough' on behalf of all our kids."

Obama has called for Congress to approve a ban on the sale in the United States of military-style assault weapons, a ban on the sale of high-capacity ammunition clips, and to ensure everyone gets a background check before they buy a gun, even if the purchase takes place at an open-air gun show currently exempt from such requirements.

For years Americans have been reluctant to impose greater restrictions on gun purchases, but the Newtown shooting has changed many minds and Obama is seeking to take advantage of the shift in attitude.

He has directed Vice President Joe Biden and a team of Cabinet officials to offer concrete proposals by next month on how to tighten gun laws and improve Americans' access to mental healthcare, strengthen school safety and address a culture that glorifies guns and violence.

Obama said he would push for these proposals early next year.

"You've started something and now I ask you to keep at it," he said.