More than 2.1 million illegal firearms sales -- including 1 million attempted purchases by convicted felons -- have been stopped in the 20 years since the enactment of the Brady Handgun Violence Prevention Act, according to a new report.

But the report released Friday by the Brady Campaign to Prevent Handgun Violence also stresses that millions of weapons are still being sold to buyers who are prohibited from owning them. Roughly 40 percent of gun purchases, including guns sold online and at gun shows by unlicensed sellers, are not subject to the background checks.

“It is clear Brady background checks work. Lives have been saved by the Brady law as we have seen the undeniable evidence showing gun homicides have decreased since the law took effect 20 years ago,” said Dan Gross, president of the Brady Campaign to Prevent Gun Violence. “We need Congress to expand Brady background checks to make it harder for criminals and other dangerous people to get guns online, in classified advertisements or at gun shows.”

Despite widespread public support for universal background checks, Congress has been unable to pass a bill implementing universal background checks.

House Democrats pledged Friday to renew the push for a bipartisan universal background check bill.

"We need to pass that bill... it's pro-Second Amendment, it doesn't take anybody's guns away. It just requires that people who purchase a firearm through commercial sale have to have a background check.... How anyone can be against that is completely beyond me." said Rep. Mike Thompson (D-Calif.), who co-authored the universal background check bill currently being considered by the House. "If the speaker would put our bill on the floor, it would take one vote to pass it."

Thompson said that 12,000 Americans have been killed by firearms since the Sandy Hook Elementary School shooting in 2012 -- roughly 30 a day. Despite national outcry for new gun control measures following the school shooting in Newtown, Conn., Congress did not pass any meaningful firearms measures last session and only four states -- Connecticut, Colorado, Delaware and New York -- enacted new background check measures.

House Minority Leader Nancy Pelosi (D-Calif.) vowed to continue the push for a House vote on the proposed universal background check bill, which she said would pass easily if given a vote.

"This will pass," Pelosi insisted, standing flanked by the family members of victims of gun violence, at a news conference Friday morning. "We are not going away."