Thai riot police used a cheap Chinese tear gas that contained an explosive powerful enough to rip craters in the ground to disperse crowds of anti-government protesters last week, an investigator said Monday.

The investigation by forensics experts and a human rights commission could explain why several protesters had limbs and feet blown off and three died in clashes last week with police, who insist they only fired tear gas into the crowd.

Investigators found that police used three types of tear gas — from China, the United States and Spain — but "relied heavily on tear gas made in China," said Pornthip Rojanasunand, director of the Central Institute of Forensic Science.

Click here for photos. (WARNING: GRAPHIC CONTENT)

Pornthip said an experiment showed that the Chinese gas contained high levels of RDX — a chemical commonly used to make bombs and not a standard component of tear gas intended for crowd control. Pornthip's institute conducted the investigation as part of a probe into the clashes by the National Human Rights Commission.

Tests at a military field over the weekend found that a Chinese-made tear gas canister fired from a shotgun left a crater 8 centimeters wide and 3 centimeters deep (3 inches wide and 1 inch deep), she said, noting that it also "left a hole in a metal pipe."

Grenades filled with the gas left even bigger craters, including one that was 16 centimeters wide and 8 centimeters deep (6 inches wide and 3 inches deep), National Human Rights Commissioner Surasi Kosolnawin was quoted as saying by The Bangkok Post.

One of the three people killed in last Tuesday's clashes was a 28-year-old woman who had a wound on her chest that was "roughly the same size" as a Chinese-made tear gas canister, Pornthip said.

She said it was too soon to tell if the Chinese tear gas caused the woman's death but it was "potentially highly damaging" and could "cause death and injuries."

Queen Sirikit, the wife of Thailand's revered monarch, presided over a cremation ceremony for the woman Monday in Bangkok, which was also attended by thousands of supporters of the anti-government People's Alliance for Democracy.

"The police and military generally use American (tear gas), but it's expensive — much more expensive," Pornthip said. "But comparatively, the American (tear gas) is safer."

Police used tear gas to clear the streets after protesters attempted to blockade Parliament to keep Prime Minister Somchai Wongsawat from delivering a policy statement. The ensuing clashes injured 478 people — mostly protesters — including 85 who were hospitalized, according to medical authorities.

Eight protesters lost legs, feet or toes in last week's clashes with riot police, sparking outrage and accusations of police brutality.

The protest alliance says it plans a large demonstration on Wednesday outside police headquarters to protest alleged police brutality in the clashes.

The protesters regard Somchai as a proxy of deposed Prime Minister Thaksin Shinawatra, a former telecommunications billionaire who was ousted by a 2006 military coup for alleged corruption and misuse of power. Somchai is a brother-in-law of Thaksin's.