SAN FRANCISCO (AP) — Google is promising to be more vigilant about preventing terrorist propaganda and other extremist videos from appearing on its YouTube site amid intensifying criticism about the internet's role in mass violence.

Its crackdown will involve both computer programs and an expanded group of people dedicated to identifying videos promoting terrorism so they can be blocked from appearing on YouTube or quickly removed.

Google is making the commitment in the wake of violent attacks in the U.S. and elsewhere. A van struck a crowd of people outside a London mosque Sunday, the second...