President Joe Biden on Saturday signed into law the first significant federal bill on gun safety in decades, saying that while it falls short of what's really needed it will "save lives."

"While this bill doesn't do everything I want, it does include actions I've long called for that are going to save lives," he said at the White House before leaving for two major diplomatic summits in Europe.

The gun legislation includes enhanced background checks for younger buyers and federal cash for states introducing "red flag" laws that allow courts to temporarily remove weapons from those considered a threat.

Billions of dollars have been allocated to crack down on "straw purchasers" who buy firearms for people not allowed to own them, and to curb gun trafficking.

However, much tougher measures wanted by Biden and other Democrats did not make it in, including a ban on military style rifles often used by the lone gunmen who typically carrying out mass shootings. Also absent is a longtime push for mandatory background checks on all gun purchases.

Reeling off a list of notorious mass shootings, Biden said the message from victims "was 'do something…, for God's sake just do something.' Well today, we did."

Referring to political gridlock in a near evenly divided Congress, Biden said the new law, which had rare strong support from both Republicans and Democrats, was "monumental."

"When it seems impossible to get anything done in Washington, we are doing something consequential," he said. "I know there's much more work to do and I'm never going to give up."

As he inked his signature on the document, Biden added again: "God willing, this is going to save a lot of lives."