'We have to act’ on gun control: Biden reacts to Colorado

"I don't need to wait another minute, let alone another hour, to take common sense steps that will save lives in the future," Biden said, adding that "we can ban assault weapons."

"This is not and should not be a partisan issue," Biden said at the White House. "It's an American issue that will save lives, American lives. We must act."

Biden spoke before leaving Washington for Columbus, Ohio, a visit where he will mark the 11th anniversary of the signing of the Affordable Care Act known as Obamacare.

The mass shooting in Boulder followed a gunman's killing the previous week of eight people at spas in Atlanta, bringing new attention to U.S. gun violence.

Flags at the White House were at half staff until sunset on Monday to commemorate the Atlanta shooting victims. They flew at full staff for a few hours on Tuesday morning before being lowered again to mark the Boulder killings.