KANDAHAR, Afghanistan — The U.S. military said Monday that an explosion that destroyed five fuel tankers parked outside its main base in southern Afghanistan was an accident, not the result of a Taliban attack.

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At least three drivers were injured in the blast early Sunday, and Afghan officials were quick to blame Taliban rebels.

But U.S. military spokeswoman Lt. Cindy Moore said the blast, which sent plumes of black smoke billowing over Kandahar, was caused by “faulty fuel tanks.”

She said military investigators determined that the blast originated inside one of the trucks, not outside.

“More than likely it was some type of problem with the tank,” she said.

The explosion took place just after 3 a.m. Sunday, while Pakistani and Afghan drivers were waiting to deliver fuel to the U.S. base at Kandahar airport.

Tight security measures mean long waits for drivers delivering fuel to U.S. bases in Afghanistan.

Meanwhile, the military said Monday that one of its CH-47 helicopters operating in the south made a “precautionary landing” near Kandahar after developing a mechanical problem. Moore said there were no injuries in the incident, which occurred early Sunday, and that the helicopter was repaired on site.