Image credit: KOMO/ABC News

An online post with a picture of a gun and a threat of violence prompted police and officials with the Issaquah School District to close Skyline High School today in Sammamish, Wash.

Shortly after 9 p.m. Wednesday, an anonymous posting from someone claiming to be a bullied student vowed to "open fire on the people in the commons in the morning until I am either taken down by our school's police officer, or until I run out of mags."

Within two hours, the threat had made its way around social media sites, prompting more than 100 calls to police and school officials.

In a late-night email to faculty and the parents of the school's 2,000 students, the school district stressed "student and staff safety is our top concern."

Sammamish police spokeswoman Sgt. Jessica Sullivan said the authorities didn't know who posted the threat or its legitimacy. She added, however, that officials were working on a number of leads.