WASHINGTON (AP) — President Joe Biden welcomed a crowd to the White House lawn Monday to showcase a new law meant to reduce gun violence, celebrating "real progress" after years of inaction. But he also lamented the country remains "awash in weapons of war" — with the 16-day-old law already overshadowed by yet another horrific mass shooting.

The bill, passed after recent gun rampages in Buffalo, New York, and Uvalde, Texas, incrementally toughens requirements for young people buying guns, denies firearms to more domestic abusers and helps local authorities temporarily take weapons from people judged to be dangerous.

But the "celebration" Monday morning came a week after a gunman in Highland Park, Illinois, killed seven people at an Independence Day parade, a stark reminder of the limitations of the new law in addressing the American phenomenon of mass gun violence. And it comes as Democratic governors have taken up the mantle of offering outrage in the face of gun violence.

Biden hosted hundreds of guests on the South Lawn, including a bipartisan group of lawmakers who crafted and supported the legislation, state and local officials — including Illinois Gov. J.B. Pritzker and Highland Park Mayor Nancy Rotering — and the families of victims of both mass shootings and everyday gun violence.

"Because of your work, your advocacy, your courage, lives will be saved today and tomorrow because of this," Biden said.

"We will not save every life from the epidemic of gun violence," he added, "But if this law had been in place years ago, even this last year, lives would have been saved."

Still, Biden said, "we're living in a country awash in weapons of war." He repeated his call on Congress to pass a federal ban on assault weapons and high capacity ammunition magazines — or at minimum to require more stringent background checks and training before purchases.

He also said Congress should pass legislation to hold gun owners legally accountable if their weapons are improperly stored and are used to commit violence. He noted that he owns four shotguns and said he keeps them secured at his home.

"We can't just stand by," Biden said. " With rights come responsibilities. If you own a weapon, you have a responsibility to secure it and keep it under lock and key."

Biden on Saturday invited Americans to share with him via text — a new White House communications strategy — their stories of how they've been affected by gun violence, tweeting that "I'm hosting a celebration of the passage of the Safer Communities Act." He told some of their stories on Monday — of people traumatized by shootings and kids left orphaned.

The new law is the the most impactful firearms-violence measure Congress has approved since enacting a now-expired assault weapons ban in 1993. Yet gun control advocates — and even White House officials — say it's premature to declare victory.

"There's simply not much to celebrate here," said Igor Volsky, director of the private group Guns Down America.

"It's historic, but it's also the very bare minimum of what Congress should do," Volsky said. "And as we were reminded by the shooting on July 4, and there's so many other gun deaths that have occurred since then, the crisis of of gun violence is just far more urgent."

Volsky's group, along with other advocacy groups, was holding a news conference on Monday outside the White House calling on Biden to create an office at the White House to address gun violence with a greater sense of urgency.

Biden has left gun control policy to his Domestic Policy Council, rather than establishing a dedicated office like the one he opened to address climate change or the gender policy council he started to promote reproductive health access.

"We have a president who really hasn't met the moment, who has chosen to act as a bystander on this issue," Volsky said. "For some reason the administration absolutely refuses to have a senior official who can drive this issue across government."

During his remarks Monday, Biden was heckled by Manuel Oliver, whose son Joaquin was killed at Marjory Stoneman Douglas High School in Parkland, Florida. Biden briefly paused his speech and asked Oliver, who was shouting, to sit down, before adding "Let him talk, let him talk," as he was escorted out of the event.

The president signed the bipartisan gun bill into law on June 25, calling it "a historic achievement" at the time.

On Monday, Biden said the law's passage should be a call for further action.

"Will we match thoughts and prayers with action?" Biden asked. "I say yes. And that's what we're doing here today."

On Friday, Biden responded to the assassination of former Japanese Prime Minister Shinzo Abe by taking note of how the shooting had shocked people in Japan. The country has a strikingly low incidence of gun violence compared to the U.S., which has experienced thousands of gun deaths already this year.

Most of the new law's $13 billion in spending would be used for bolstering mental health programs and for schools, which have been targeted by shooters in Newtown, Connecticut, and Parkland. The law was the product of weeks of closed-door negotiations by a bipartisan group of senators who emerged with a compromise.

It does not include far tougher restrictions that Democrats and Biden have long championed, such as a ban on assault-type weapons and background checks for all gun transactions. Prospects are slim for any further congressional action this year.