Pelosi calls for 'balance' between free speech and safety after Buffalo shooting

House Speaker Nancy Pelosi said Sunday that social media companies have to address and track down extremism on their platforms.

House Speaker Nancy Pelosi said Sunday that social media companies have to address and track down extremism on their platforms, after a gunman who reportedly espoused white supremacist ideology opened fire at a Buffalo, New York, supermarket on Saturday, killing at least 10.

Among the 13 victims shot, 11 were Black and two were white, authorities said.

"There has to be vigilance," Pelosi, D-Calif., told ABC "This Week" anchor George Stephanopoulos. "People have to alert other authorities if they think that someone is on a path to domestic terrorism, to violence of any kind."

Investigators are looking at multiple online postings that may be associated with the shooter, 18-year-old Payton Gendron, that include praise for South Carolina church shooter Dylann Roof and the New Zealand mosque shooter Brenton Tarrant, sources told ABC News.