School officials said the bus was used Monday and Tuesday to transport students to Rock Ridge High School, and Buffalo Trail and Pinebrook Elementary schools.

The stable material never endangered students, authorities said.

Here is the text of the announcement:

In response to the incident, the Loudoun County Sheriff's Office and the Loudoun County Fire Marshal's announced that this particular training program has been suspended until a thorough review of all procedures is completed.

During a joint meeting on March 31, 2016, representatives from the Loudoun County Sheriff's Office, the Loudoun County Fire Marshal's Office, the Loudoun County Public Schools' Safety and Security Office, and the Office of the County Administrator met with personnel from the CIA to discuss a recent K9 training exercise where benign explosive training material was determined to have been left inside a Loudoun County Public School bus. Both the Loudoun County Fire Marshal's Office and the Loudoun County Sheriff's Office, in cooperation with the Loudoun County Public School System, are recipients of the CIA K9 training.

On March 30, 2016, the training material was located inside the engine compartment of a Loudoun County Public School bus during routine maintenance work. Personnel from the Loudoun County Sheriff's Office and the Loudoun County Fire Marshal's Office responded to the Loudoun County Vehicle Maintenance Facility on Loudoun Center Place in Leesburg, Va. to determine the source of the materials.

The material was determined to have been used during a recent joint canine training led by the CIA at Briar Woods High School in Ashburn, Va. during the week of Spring Break (March 21-March 24). Similar training is conducted with other local public safety and federal agencies in the region throughout the year.

As part of the training exercise last week, canine explosive detection training was conducted in areas inside and outside of the high school. During the outside portion of the training, the training material was hidden inside an engine compartment of the bus. At some point, a portion of the material from the container appears to have been dislodged from the container and fell into the engine compartment of the bus and was not recovered following the training.