The State Administration of Work Safety released an investigative report online on Friday about a fatal traffic accident last year.

The report said that the main reason behind an accident involving a bus that killed 36 people in Shaanxi province last year was the driver's fatigue.

A sleeper bus with 39 people onboard rammed into a tanker carrying methanol — a highly flammable liquid — at 2:30 am on Aug 26, 2012, on a highway in Yan'an, Shaanxi province.

The bus caught fire, killing 36 and injuring three people. The direct economic losses reached 31.61 million yuan ($5.27 million).

After a seven-month investigation, the administration said that the bus driver Chen Qiang, 41, didn't follow the rules of not driving between 2 am and 5 am.

Also, the tanker driver was driving too slowly on the expressway, causing the sleeper bus to ram into it, the report said.

The report added that the weather was clear and the road was in good condition.

The two bus drivers, both dead, and two truck drivers showed no signs of alcohol or drugs.

Twenty-six Party officials in He'nan, Shaanxi province, and in the Inner Mongolia autonomous region have been suggested for disciplinary punishment.

The report also listed 10 suspects who were arrested and are subject to criminal liability.