LITTLETON, Colo. (AP) Colorado Gov. Jared Polis says the threat that prompted a lockdown at Columbine High School and other Denver-area schools involved someone who was armed and "may be interested in harming our schools or our kids."
Polis said Tuesday the Colorado Department of Public Safety was working with the FBI to protect public safety.
He said he had no other information.
The Department of Public Safety urged schools urged schools to tighten security, and more than 20 put lockdowns in place.
The lockdowns come just days before the 20th anniversary of a mass shooting at Columbine High School that killed 12 students and a teacher. Authorities say they are looking for a woman suspected of making threats. They say she should be considered armed and extremely dangerous.