LOUDOUN COUNTY, Va. — Explosive training material was inadvertently left in a school bus after a training exercise at a local high school, and recovered soon afterward with no threat to any passengers aboard.

The Central Intelligence Agency (CIA) left a benign explosive training material inside the engine compartment of a Loudoun County Public Schools bus at Briar Woods High School during a K-9 training exercise it conducted from March 21 to 24 during the district’s spring break, according to a press release from the Loudoun County Sheriff’s Office.

The Loudoun County Fire Marshal’s Office and the sheriff’s office — with the cooperation of the school district — are participants in the CIA K-9 training, according to a press release from Loudoun County Public Schools.

As part of the exercise, 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 to have fallen into the engine compartment of the bus, and was not recovered following the training.

School district spokesman Wayde Byard described the explosive material to The Washington Post as a “putty-type” material that requires a special detonator and is designed for use on the battlefield.

The bus in which the missing training material was found underwent routine preventive maintenance on Wednesday afternoon, after having been in service on Monday and Tuesday of last week; it made eight runs, carrying 26 students to and from three schools, according to the school district.

The CIA released a statement on Thursday that said it coordinated with local authorities to recover the material after it was notified on Wednesday that the material was found, and has accounted for all the explosive training material used in the K-9 training program.

The CIA and Loudoun County explosive experts said that the training materials used in the exercises are stable, and the students on the bus were not in any danger from the material.

As a precaution, on Wednesday night, all buses that were used or were located near the training exercise at the high school were further searched, and no further traces of the training material were found, according to the sheriff’s office.

In addition to a general announcement to all students, parents and staff, on Wednesday night, the principals of the three affected schools did outreach calls to students of the affected bus.

Officials are continuing review of the incident.

The statement released by the CIA also said that to prevent future such incidents, it has taken immediate steps to strengthen inventory and control procedures in its K-9 program, and will conduct an independent review of its K-9 training program.