The biggest wildfire in Texas state history, which killed two people and scorched more than 1m acres, was caused by a power line pole that had decayed at the base, an investigation has concluded.

The finding comes from a Texas A&M forest service investigation into the Smokehouse Creek fire, which blazed through the state’s Panhandle region and into neighbouring Oklahoma after breaking out near the small town of Stinnett on 26 February.

Related: Xcel Energy admits it was ‘involved in ignition’ of Texas’s Smokehouse Creek fire

The investigation report described how “[a] power pole that appeared to be decayed at the base where it made contact with ground had broken off at ground level”. Winds of up to 60mph and unseasonably high temperatures had been reported when the blaze started.

The forest service report did not elaborate on what led to the power line igniting the blaze.

Its conclusion comes after the utility provider, Xcel Energy, issued a statement acknowledging that “its facilities appear to have been involved in the ignition of the Smokehouse Creek fires”.

However, the Minnesota-based company has denied that it has been negligent in maintaining the structures or allowing them to decay.

Xcel Energy is subject to a lawsuit filed on behalf of a homeowner in Stinnett alleging that the fire started “when a wooden pole defendants failed to properly inspect, maintain and replace, splintered and snapped off at its base”.

Xcel has disputed the allegations. However, Mikal Watts, the attorney who filed the suit on the homeowner’s behalf, said in a statement issued this week that the company conducting inspections for Xcel had previously found the pole’s condition to be so unsafe that it had marked it with a red tag, indicating that it should not be climbed and should be replaced immediately.

Some 500 structures have been destroyed and thousands of livestock have been killed in the blaze, which was reported by Texas forest A&M service to be 87% under control on Friday.

Two women were killed, one who was overcome by flames after leaving her truck and another whose remains were found in her home in Stinnett.

Another power line is said to have caused a separate wildfire in the Panhandle region, the Windy Deuce fire, which ignited on 26 February at an oil field. It is believed to have been sparked by a power line that ran directly through a tree and made contact with tree limbs, according to a forest service report.