Europe's security body has renewed calls for an independent inquiry into last month's crackdown on protesters in the Uzbek city of Andijan.
Human Rights Watch described the events as a "massacre"
The Organisation for Security and Co-operation in Europe (OSCE) said the investigation was needed to get a "full picture" of what happened on 13 May.
It has issued a report saying between 300-500 people died when troops fired on a rally. Tashkent says 173 died.
The victims' families have been marking the 40th day since the violence.
It is a local Islamic tradition of remembering the dead, the BBC's Steven Eke says.
There are still disputed versions of what happened in Andijan, with the Uzbek government insisting that the eastern city saw an attempt by radical Islamists to seize power.
Leading human rights groups say many hundreds of civilians were deliberately killed in what Human Rights Watch said was a "massacre".
The OSCE called for an "independent, credible, international investigation".
"As long as there is no international investigation, with access to Andijan, we do not have the full picture," OSCE chairman Dimitrij Rupel said in a statement.
President Karimov has said civilians were not harmed on 13 May
OSCE based its report on 44 in-depth interviews with people who fled Andijan after the violence. The organisation had no access to the city itself.
The report concluded that "force was used repeatedly against unarmed civilians throughout the day".
It said it "was indiscriminate and disproportionate, and that many unarmed civilians were wounded or killed".
The few reports coming from Andijan speak of a sombre atmosphere, with the relatives of those who died reluctant to speak about how they are marking Forty Days, our correspondent says.
Officials on powerful neighbourhood committees have reportedly told ordinary people not to hold open ceremonies.
Yet the relatives of policemen or government forces who were killed are marking their losses publicly, our correspondent says.
He says that since the events, Andijan is now effectively off-limits, sealed from foreign, especially Western, eyes and ears.
Our correspondent says the US-Uzbek strategic partnership, once lauded by both sides, is tattered, with Uzbekistan's leaders looking instead to Russia and China for public support.
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 other soldiers in buildings along the road shoot at the crowd too
Source: Human Rights Watch