HOUSTON - Hoax bomb threats issued on social media prompted evacuations at three separate high schools in the US 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.