BAGHDAD, Iraq (CNN) -- American soldiers discovered a girls school being built north of Baghdad had become an explosives-rigged "death trap," the U.S. military said Thursday.
The plot at the Huda Girls' school in Tarmiya was a "sophisticated and premeditated attempt to inflict massive casualties on our most innocent victims," military spokesman Maj. Gen. William Caldwell said.
The military suspects the plot was the work of al Qaeda, because of its nature and sophistication, Caldwell said in an interview with CNN's Wolf Blitzer.
The plot was uncovered Saturday, when troopers in the Salaheddin province found detonating wire across the street from the school. They picked up the wire and followed its trail, which led to the school. Once inside, they found an explosive-filled propane tank buried beneath the floor. There were artillery shells built into the ceiling and floor, and another propane tank was found, the military said.
The wire was concealed with mortar and concrete, and the propane tanks had been covered with brick and hidden underneath the floor, according to a military statement. Soldiers were able to clear the building.
"It was truly just an incredibly ugly, dirty kind of vicious killing that would have gone on here," Caldwell said.
Iraqi contractors were responsible for building the school, which was intended to bring in hundreds of girls.
"Given the care and work put into emplacing this IED, it is likely it had been planned for a long time" and it is thought that "the IED was not intended to be set off until the building was occupied," the military said.
Authorities intend to question the Iraqis involved in the school's construction.