Sun Huashan, deputy director of the State Administration for Work Safety, speaking on state television, didn't say who might be punished for the Dec. 23 disaster or what penalty they might face.
Fumes that gushed from a burst gas well spread across a mountainous area northeast of the city of Chongqing, killing villagers as they slept or tried to flee. It was China's worst recent industrial disaster.
"This was an accident due to negligence," Sun said. "Those people who were responsible will be dealt with."
The government had earlier blamed an unspecified drilling accident.
Investigators concluded that the drilling crew improperly dismantled anti-blowout equipment, misjudged the amount of gas in the well and failed to spot the blowout, Sun said.
After the fumes began to flow from the well, the crew failed to ignite them, which would have prevented them from spreading, Sun said.
Emergency crews plugged the well on Dec. 27.
Tens of thousands of people were evacuated from surrounding villages but have since been allowed to return home.
A poisonous mix of natural gas and hydrogen sulfide had erupted from the well in the remote mountain town of Gaoqiao, leaving a 25-square-kilometer (10-square-mile) "death zone" strewn with bodies of adults and children.
Emergency workers couldn't enter the area until more than a day after the gas started flowing because they lacked the proper safety equipment. When they finally did go in, they found villages filled with dead.
Thousands of people were treated for gas poisoning. Crews spent days testing water and plant life for toxins before people were allowed to go home.
The death toll was high even by the standards of accident-plagued Chinese industry, where thousands of people are killed every year in coal mine explosions and other disasters. Two of those killed were gas field employees, the official Xinhua News Agency has reported.
The gas field belongs to the state-owned China National Petroleum Corp. A CNPC subsidiary, PetroChina, began building a US$400 million pipeline in August to pump natural gas from Chongqing to central China.