An explosion at an Arizona power plant Wednesday morning was caused by a makeshift bomb, police tell Fox News.

The explosion, which is being investigated by the FBI, took place around 9:30 a.m. Wednesday at the UniSource Energy Services Valencia Plant in Nogales. The device ruptured a diesel storage tank and caused a spill, but the fuel didn’t ignite, police said.

“Preliminary investigation determined that an incendiary-type device was found next to a large capacity fuel tank,” said Nogales Police Lt. Carlos Jimenez, a department spokesman.

The device “failed to compromise the tank,” according to Jimenez. The plant, as well as surrounding businesses, was evacuated.

Jimenez says there were no injuries reported at the scene. Police are looking for suspects and witnesses to the explosion, but there are no leads.

“The Arizona Department of Public Safety, Federal Bureau of Investigation, and the Alcohol, Tobacco and Firearms Investigative Unit were contacted to assist in the investigation,” said Jimenez.

UniSource Energy Services provides energy to approximately 237,000 customers in Arizona, according to the company website. Those customers did not experience any power outages or disruption of services.

Fox News’ Aalia Shaheed and The Associated Press contributed to this report.