Schools on heightened alert after threat locks down Columbine

Public schools in Denver will be closed on Wednesday after a young woman said to be "infatuated" with the 1999 Columbine High School massacre made threats just days before its 20th anniversary.

Police are looking for Sol Pais, 18, who is thought to have made undisclosed threats that prompted Columbine and more than 20 other schools outside Denver in the US state of Colorado to lock their doors for nearly three hours on Tuesday afternoon.

All schools in the Denver area were urged to tighten security because the threat was deemed "credible and general", said Patricia Billinger, a spokeswoman for the Colorado department of public safety.

The Jefferson County sheriff's office and the FBI said Pais travelled to Colorado from Miami, Florida, on Monday night and bought a pump-action shotgun and ammunition.

Denver Public Schools said that all facilities and programmes will be closed on Wednesday, and there will be no afternoon activities or athletic competitions.

The district said the decision to close campuses was in collaboration with other Denver metro-area school districts due to the ongoing safety concern.

On Tuesday, some schools released their students after additional security was called in, and cancelled evening activities or moved them inside.

"We always have heightened awareness close to high-profile anniversaries like this," Ms Billinger said.

Pais was last seen in the foothills west of Denver, is considered armed and extremely dangerous and should not be approached, authorities said.

Dean Phillips, special agent in charge of the FBI in Denver, said: "This has become a massive manhunt ... and every law enforcement agency is participating and helping in this effort."

The FBI's Rocky Mountain Safe Streets Task Force issued a notice describing Pais as "infatuated with (the) Columbine school shooting".

The alert also said police who come into contact with her should detain her and evaluate her mental health.

Sheriff's spokesman Mike Taplin said the threats she made were general and not specific to any school.

The Denver Post reported that a call to a phone number listed for Pais' parents in Surfside, Florida, was interrupted by a man who identified himself as an FBI agent and said he was interviewing them.

The doors were locked at Columbine and more than 20 other schools in the Denver area as the sheriff's office said it was investigating threats against schools related to an FBI investigation.

Columbine students continued attending classes in the afternoon and left school on time, but after-school activities were cancelled on the campus in Littleton, Colorado.

Two teenage gunmen attacked Columbine on April 20 1999, killing 12 classmates and a teacher.

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