Human Rights Watch has called on the international community to hold Uzbekistan to account over its violent crackdown in Andijan a year ago.
The dead were being picked up by relatives for days
"The need for a co-ordinated and forceful international response to the Andijan massacre is more urgent than ever," said the US human rights group.
Although details remain unclear, it is thought hundreds of people may have been killed on 13 May last year.
The crackdown in Andijan town square followed an uprising and jailbreak.
The Uzbek president, Islam Karimov, has repeatedly rejected calls for an inquiry, insisting the demonstrators were armed Islamic militants.
"The Uzbek government has done nothing to hold the perpetrators of this atrocity accountable, and the international community has failed to compel the Uzbek authorities do so. The victims deserve no less than full justice," HRW executive director Kenneth Roth said on Thursday.
The group called on the EU and US to expand diplomatic and economic sanctions imposed on Uzbek leaders after the violence.
Climate of fear
HRW says Uzbek authorities have launched a "fierce crackdown" on political opponents, activists and journalists trying to investigate the events of 13 May 2005.
In the past year the BBC has been prevented from working freely in Uzbekistan.
Our correspondent Natalia Antelava, in neighbouring Kyrgyzstan, says traders who manage to cross the border tell of dire economic conditions within Uzbekistan.
Those who dare to speak out more openly describe a climate of fear, she says - with one woman comparing Uzbekistan to the Soviet Union under Joseph Stalin.
"People are just terrified. They have so much pain in their hearts, they are afraid to let it out," said a woman who refused to give her name.
"Being a relative of someone who has died in Andijan means security can knock on your door at any time and take you away," she told the BBC.
The UN says hundreds of Uzbeks have fled the country over the past year.
Once out, many of them tell stories of mass graves in Andijan, and about the routine practice of torture in prisons.
Many of them say they have relatives who have simply disappeared.
Human rights groups have condemned not just the Uzbek authorities, but also what they say is the failure of the West to respond.