Authorities in Colorado are on the lookout for an “armed” 18-year-old woman believed “to be extremely dangerous” after several schools were put on lockouts earlier Tuesday.

"Lockout means biz as usual inside buildings, entry/exit restricted," Jeffco public schools tweeted.

The Jefferson County Sheriff’s Office, along with the FBI’s Denver office, posted a plea on Twitter for information about Sol Pais, who they said made her way to Colorado on Monday night and “made threats.”

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Authorities described her as a white female with brown hair who is about five-foot-five-inches tall. She was last spotted “in the foothills of Jefferson County” and was wearing a black t-shirt, camouflage pants and black boots, officials said.

The message to the public came hours after the sheriff’s office tweeted that they were probing what looked like “a credible threat possibly involving schools.” As a result, numerous schools in the Columbine area and Mountains were on a lockout, officials said, adding that all of the students were safe and authorities were on site.

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Among them was Columbine High School, school officials said on Twitter. The situation arose days ahead of the 20th anniversary of the deadly shooting that occurred there on April 20, 1999.

Authorities urged anyone with information to call the FBI tip line at (303) 630-6227 and cautioned against approaching the woman.

The Associated Press contributed to this report.