Photo taken on July 22, 2011 shows the burnt double-deck bus in Xinyang of central China's Henan Province. [Xinhua]

Illegally transported inflammable chemicals directly caused the fatal double-decker bus fire that killed 41 passengers and injured six others last month in Xinyang, central China's Henan Province, according to an investigation by authorities.

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Investigators delivered a report on the accident to a special inspection team consisting of members from several organs of the State Council and the local governments of Shandong and Henan provinces at a meeting on Tuesday.

According to the report, a further police investigation has led to the detainment of another three suspects, in addition to the six suspects already in police custody.

It is a violation of the packaging and traffic code to use passenger vehicles to ship inflammable and explosive chemicals that should be transported via refrigerated vans, according to the report.

The 35-seat bus, which was traveling from the city of Weihai in eastern Shandong Province to central Hunan's provincial capital Changsha, caught fire in the wee hours of July 22 on the Beijing-Zhuhai Expressway.

Addressing the meeting Tuesday, Wang Dexue, deputy director of the State Administration of Work Safety and also head of the State Council inspection team, said that management practices that contributed to the fire should also be investigated thoroughly, adding that those responsible will be held accountable in strict accordance with the law.

Wang also said the deadly accident should serve as a lesson and lead to greater efforts and vigilance to prevent similar tragedies.