Uzbekistan's crackdown on protesters in Andijan last month was a "massacre", according to Human Rights Watch, in the fullest report yet on the bloodshed.
President Karimov says civilians were not harmed on 13 May
The US-based rights group called for Washington and the EU to suspend links with the Uzbek government until it allows an independent investigation.
Tashkent says only 173 people, mainly Islamic militants, died in the protest.
But eyewitnesses say hundreds of protesters were killed when troops opened fire on Andijan's main square.
"The scale of this killing was so extensive, and its nature was so indiscriminate and disproportionate, that it can best be described as a massacre," Human Rights Watch [HRW] said in its report, presented at a press conference in Moscow on Tuesday.
The group's assessment was based on interviews with more than 50 witnesses, most of which had fled to Kyrgyzstan.
As has been reported previously, HRW said the huge protest was sparked by the trial of 23 local businessmen on charges of religious extremism and the subsequent freeing of those men and other prisoners by armed locals on the night of 12 May.
But it said there was no evidence that the protest was motivated by an Islamist agenda, as alleged by the government.
"Interviews with numerous people present at the demonstrations consistently revealed that the protesters spoke about economic conditions in Andijan, government repression, and unfair trials - and not the creation of an Islamic state. People were shouting 'Ozodliq!' ['Freedom'] and not 'Allahu Akbar' ['God is Great']," HRW said.
Witnesses told the group that they massed in Andijan's main square, calling for freedom and justice, and were then gunned down by government troops after the square was sealed off.
Escape route 'blocked'
The protesters tried to flee the square, and fled north, but found their way blocked and came under heavy fire near School 15, the report said.
The government says it is conducting its own investigation into what happened.
A few days after the bloodshed, it arranged for foreign diplomats to visit Andijan, but the visitors said their tour was tightly constrained.
HRW said that, on the basis of its interviews with witnesses, it believed hundreds of people died during the 13 May crackdown.
The Uzbek embassy in London did not respond to a request for an interview regarding the HRW report.
1. Crowd masses on Bobur Square, which is later sealed off by security forces
2. Troops open fire on crowd as helicopters circle, forcing people to flee north to Cholpon Prospect
3. Crowd pushes aside buses set up to block the road, as shooting continues
4. Crowd comes face to face with troops near School 15, who open fire as othe soldiers in buildings along the road shoot at the crowd too
Source: Human Rights Watch