A chain of messages posted to an anonymous chat board known for its explicit conversation threads and graphic images included an ominous warning on Wednesday evening not to go to school on Thursday "if you are in the northwest."

The anonymous postings and numerous replies appeared on the site 4chan.org hours before a 20-year-old gunman opened fire at Umpqua Community College in Roseburg, Oregon, on Thursday, killing and wounding a number of people.

Reuters viewed the thread but could not verify its authenticity or whether it had any connection to Thursday's shooting. Emailed questions to federal law enforcement officials about the postings were not immediately answered.