An international human rights group urged Thailand on Tuesday to properly investigate dozens of deaths during a military crackdown on anti-government protests last year, and said the lack of criminal trials showed the army continues to have impunity.

New York-based Human Rights Watch issued a report saying the army had used snipers to shoot protesters, killing unarmed participants and volunteer paramedics.

In one incident, charged Brad Adams, the group's director for Asia, the army's actions amounted to "cold-blooded acts of murder."

"Human Rights Watch concludes that there will be no rule of law and there will be no respect for human rights so long as the military remains above the law in Thailand," he said.

Adams suggested the government could ease current political tensions by speeding up the investigation into the killings and making sure the results are credible.

A total of 91 people died in street confrontations that culminated in the military crackdown last May.

Adams was critical as well of actions by the "Red Shirt" protesters, also known as the United Front for Democracy Against Dictatorship. The group was supported by armed militants dressed in black, and some Red Shirt leaders called for the use of violence including arson.

On May 19, after the protest leaders surrendered as heavily armed soldiers cleared the streets, a major shopping complex at the protest site was set ablaze by unidentified people. More than two dozen other buildings around Bangkok, including the stock exchange, were also set alight.

Many Red Shirts were arrested and some remain in custody, but no government officials or soldiers have been charged in connection with the violence, Adams said.

Many Red Shirts support former Prime Minister Thaksin Shinawatra, who was deposed by a military coup in 2006 for alleged corruption and disrespect for the monarchy. They were demanding that current Prime Minister Abhisit Vejjajiva call early elections, charging that he came to power with the connivance of the military.

Adams highlighted an incident at Wat Pathum Wanaram, a Buddhist temple where protesters took shelter during the May 19 dispersal by the army.

He said his organization's investigation had discovered no weapons in the temple, but found that soldiers "fired repeatedly and indiscriminately" into the temple either from the ground or from a nearby elevated train line. Six bodies were found in the temple, including a nurse who had volunteered for medical duties with the Red Shirts.

"These were, as far as we're concerned, cold-blooded acts of murder," Adams said. "When a soldier who is acting as a sniper looks through his scope and pulls the trigger on a person who is not armed, that's murder, even though he is acting under the cover of government authority."