Hoax bomb threats issued on social media prompted evacuations at three separate high schools in the U.S. state of Oklahoma Friday. School officials at Booker T. Washington High School in Tulsa city, east Oklahoma, learned of a bomb threat on Twitter Thursday evening and sent all students arriving at school Friday morning to a field house while police made a sweep of the campus, local newspaper Tulsa World reported. Hours later the school was cleared when no bomb was found and classes were resumed, according to the report. Similarly, a bomb threat was reported by a faculty member Friday morning at another high school in Colcord, about 130 km away from Tulsa. Students were evacuated and sent to a gymnasium where parents picked them up. The incident also turned out to be a false alarm after police found no threat in the school. A third threat prompted evacuations at Charles Page High School in Tulsa later in the day, and again, police found no sign of a bomb, the report said. The FBI has reportedly been notified of the bomb threats and will investigate. It's not immediately known if the three incidents were related.