But it says interviews it conducted with 50 eyewitnesses and victims corroborate earlier reports that the Uzbek government used indiscriminate force against large numbers of unarmed people.
The witness accounts describe the circumstances of a massacre, says Allison Gill, a Human Rights Watch expert on Uzbekistan who helped with the report.
"We tried to provide as clear a picture as we could establish of what happened -- and I think it's probably the most comprehensive picture to date of what happened -- to show that there were very serious crimes committed by the government and a lot of unanswered questions still," Gill says. "There has to be transparency and accountability around the government's use of force on civilians."
Gill tells RFE/RL that the report does not provide an estimate of casualties or the size of the crowd that gathered in a main Andijon square ahead of the arrival of government troops. But the report suggests the death toll is far higher than the official government figure of 173 dead. For example, numerous witnesses told the organization that one group of fleeing protesters numbering close to 400 people was almost completely mowed down by gunfire from government forces.
Human Rights Watch researchers combined eyewitness accounts with numerous photographs of the protest in Bobur Square taken by journalists. The photos confirmed there was a large civilian crowd in the square, including many women and children.
Gill says the photographs also show a small number of gunmen outside the crowd and away from protesters.
"The mass of people that had gathered in the square were, in fact, peaceful demonstrators -- not part of the original group of attackers, who committed a crime, to be sure, but I think [they] were a small group, relative to the mass number of people that had gathered," Gill says.
The Uzbek government blames the incident on Islamic radicals after gunmen raided government installations and overran a prison, releasing inmates.
It says the gunmen used civilians as human shields, placing their fighters amidst a crowd of elderly citizens, women, and children.
The Human Rights Watch report confirms the raid on government facilities. But it disputes the government charge that Muslim extremists were behind the uprising.
The report says the events appear to have been sparked by the trial of 23 businessmen accused of Islamic extremism. But researcher Gill says the charges lacked evidence and that the protest in Andijon grew into a large rally of people voicing anger about poverty and government repression:
"There is no evidence of an Islamic agenda of the people that we talked to," Gill says. "There is no evidence of an Islamic agenda witnessed by any of the many eyewitnesses of the events. And it's a very, very convenient excuse for the government, and we've seen the government use it many times before."
The Uzbek Embassy in Washington was closed when the HRW report was issued, so no comment was available. But Kamran Aliyev, a Tashkent-based independent political analyst, says the government never responds to such reports.
"The Uzbek government has never reacted to critical conclusions of any international organizations, be it Transparency International, Amnesty International, or other democratic nongovernmental organizations," Aliyev says. "The Uzbek government has never reacted to their reports. In this case [of the HRW report], the Uzbek government is going to follow the same pattern and ignore the report completely, or it may criticize HRW and their conclusions through other means, [such as the Uzbek media]."
The Uzbek parliament has formed a commission tasked with thoroughly investigating the tragedy in Andijon.
Human Rights Watch is calling for an independent international inquiry into the killings, a request that has already been rejected by the Uzbek authorities.
(NCA's Gulnoza Saidazimova contributed to this report.)