Kai Ranaglia-Nelson

A Pinal County man was arrested for sexual extortion of two teenage girls after a four-month investigation that began in Australia, officials say.

The Pinal County Sheriff’s Office arrested 18-year-old Kai Ranaglia-Nelson Wednesday morning in his Coolidge home after being alerted by Australian authorities.

Two girls in Australia, ages 13 and 14, told authorities they exchanged inappropriate photos with Ranaglia-Nelson, who then threatened to expose the images if the girls didn't continue sending more, according to a press release from the Pinal County Sheriff's Office.

Ranaglia-Nelson allegedly did publicize a photo after one of the teens stopped sending more.

The sheriff's press release says Ranaglia-Nelson admitted to extorting the girls. This is an ongoing investigation with more possible victims.

Contact reporter Danyelle Khmara at dkhmara@tucson.com or 573-4223. On Twitter: @DanyelleKhmara