Visitors have been barred from Newtown High School in Connecticut for the afternoon after school officials discovered a threat on social media.
Schools Superintendent Joseph Erardi sent an email to parents Tuesday notifying them of the lock-in at the high school.
The lock-in allows classes to continue on a normal schedule, but increases security and prevents visitors from entering the building.
The threat follows an evacuation last month at the temporary Sandy Hook Elementary School in Monroe following a threat received there.
A December 2012 shooting at the former Sandy Hook school building left 20 students and six staff members dead.
Copyright AP - Associated Press
