BARTOW, Fla. -- Two middle-school girls -- ages 11 and 12 -- brought knives to their Florida school in a foiled plot to kill classmates, cut them up and drink their blood before killing themselves, police officials said Wednesday. "They told us they were Satan worshipers," Bartow Police Chief Joe Hall said, CBS affiliate WKMG reported.

The girls planned to stake out a bathroom at Bartow Middle School and wait for smaller students to enter, according to a police affidavit. They planned to cut their victims' throats, cut up their bodies and eat the flesh, authorities said. The students then planned to fatally stab themselves.

"The plan was to kill at least 1 student but were hoping to kill anywhere from 15-25 students," the affidavit said. "Killing all of these students was in hopes it would make them worse sinners ensuring that after they committed suicide ... (they) would go to hell so they could be with satan."

Get Breaking News Delivered to Your Inbox

Detectives said the girls devised the plot while watching "scary" movies at one of their houses over the weekend. Detectives said the girls posted information about the planned attack on social media. Messages on their cellphones also stated they wanted to leave body parts at the school's entrance, WKMB reported.

The alleged plot was foiled when administrators searched for them after they didn't show up for class Tuesday. The administrators found them in a bathroom stall and brought them back to their offices where they found the girls in possession of four knives, a pizza cutter and a knife sharpener, police said.

After their arrest, the girls were sent to a juvenile detention facility.

"School staff quickly responded to a report of suspicious behavior; the students were taken into custody, and no one was harmed," school officials said in a tweet.

The girls face charges of conspiracy to commit first-degree murder and possession of a weapon at school, among other charges. It will be up to prosecutors to decide whether the girls will be charged formally as juveniles or adults, Deputy Police Chief Bryan Dorman said in an email.

Officials with Polk County Schools said that extra police officers and guidance counselors would be at the school this week.