A motor vehicle explosion and fire that rocked the grounds outside the Blaine House in Augusta last week was the result of a lithium ion battery failure, the State Fire Marshal’s Office announced Sunday night.

Witnesses reported seeing smoke coming from a 2015 Chevrolet Silverado before it exploded into flames around 2:30 p.m. Thursday.

Gov. Janet Mills was across the street in the State House at the time, participating in a ceremony to honor Maine’s County Teachers of the Year.

No one was injured, but an explosion so close to the governor’s mansion attracted a lot of attention. Investigators determined that the pickup truck had been legally parked on Chamberlain Street since 7:30 a.m. and said the incident was not believed to be suspicious.

In a news release issued Sunday evening, Shannon Moss, spokesperson for the State Fire Marshal’s Office, said investigators determined the explosion and fire were caused by the failure of a lithium ion battery that was attached to a cordless drill in the back of the pickup truck.

“The Fire Marshal’s Office says that while instances of these fires or explosions are infrequent, spontaneous combustion of lithium-ion batteries does occur,” Moss said.

The State Fire Marshal’s Office said reasons for battery failure could include mechanical defects, poor design or an external factor, such as leaving a battery in a hot area or direct sunlight for extended periods.

“Given the extent of the fire damage, investigators are not able to pinpoint exactly what caused this battery to fail,” Moss said.

The pickup truck was destroyed by the explosion and fire.

Lithium ion batteries are known to have a “high energy density” for their size, according to the Environmental Protection Agency, leading to increased demand for their use in products such as toys, wireless headphones, handheld power tools, small and large appliances, electric vehicles, and electrical energy storage systems.