A 15-year-old student at Duncan High School in southern Oklahoma was arrested after threatening to shoot his classmates, authorities say.

An unidentified person posted several threats to the Yik Yak app  saying they were going to to bring a gun to school to shoot students. Police began investigating the posts.

Yik Yak is an app that allows users to make anonymous posts. It is similar Twitter, but doesn't include users' names.so when one posts, no one knows who they really are.

According to a police statement, three of the Yik Yak posts stated:

"Bring my 9 mm with me to school tomorrow. All white boys gets bullets."

"Rednecks dying first at DHS."

"Don't come to school tomorrow if you're innocent. Shooting Duncan High."

Extra police were on duty Thursday morning as students arrived for class at the high school. According to KATV, police say they plan to issue additional search warrants later Thursday.

Last year, an Oklahoma teen was convicted in a plot to kill students, teachers and police officers. Authorities say the teenager tried to recruit classmates for a mass shooting and bomb attack at Bartlesville in northeastern Oklahoma. The 19-year-old was recommended a 30-month prison term and a $5,000 fine for planning to cause bodily harm. He pleaded not guilty, stating that he was only joking when he told his classmates about a bomb attack and shooting. A few hours before the Sandy Hook Elementary tragedy in Newtown Connecticut that swept the nation with grief happened, the boy was arrested.

In January 2014, The University of Oklahoma in Norman briefly shut down after receiving a report of a possible shooting. It turned out to be a false alarm. On the day of the report, no evidence of any shots being fired had been found.