"After more than three days' efforts, we found self-ignition of the explosives led to the explosion," the investigators of the July 4 karaoke bar explosion concluded in a terse brochure made available to Xinhua Sunday.

No more details were given.

The explosion occurred at the Tianying karaoke bar in Tianshifu Township of Benxi Autonomous County of Manchu Nationality in Liaoning on Wednesday night, killing 25 people on the spot and injuring 41 more. The explosion also leveled the two-storey entertainment venue to the ground and damaged some nearby buildings.

The 25 dead victims included the bar owner Qu Yijie - known locally as Qu Hua - his elder brother and his elder brother's wife, said Fu Qingbin, a spokesman for the Benxi county government.

More than 10 teenage girls were celebrating a birthday for a 19-year-old girl Sun Bo, who worked at a nearby department store and most of them died in the blast, including Sun herself, Fu said.

The victims also included a motorcycle driver and a truck driver who were passing the door of the KTV bar and a couple who owned a nearby carwash shop, he said.

The relatives of the victims have been arranged to stay in local hotels, waiting to discuss the issue of compensation with local authorities.

The 41 people injured in the blast are still being treated in local hospitals and are in a stable condition, local health authorities said.

Four people suffered serious injuries, while 37 others suffered fractures, chest injuries and broken ribs, said a physician.

One seriously wounded person has been transferred to Benxi City Central Hospital. The others are either in Benxi County No. 1 hospital or at a hospital in Tianshifu Township, said Jiang Yongcheng, deputy director of the Benxi County Health Bureau.

A dozen medical experts have gone to Benxi County to help treat the victims.

Police questioned the parlor owner's wife and some employees of the parlor in order to establish the cause of the fatal blast.