The US has said Uzbekistan still owes an explanation for the killing of civilians by soldiers in the city of Andijan on 13 May one year ago.
There are starkly different version of the events of 13 May 2005
The State Department repeated calls for an international inquiry into what relatives said was the machine gunning of a crowd without warning.
The Uzbek government says troops were eliminating a dangerous group of Islamic extremists.
There will be no official events to mark the anniversary in Uzbekistan.
US State Department spokesman Sean McCormack said: "Numerous eyewitness reports of security forces shooting and killing several hundred men, women and children have not been adequately addressed."
He called for an international investigation and urged the central Asian republic to uphold its "international human rights commitments".
Two Republican legislators began moves towards sanctions this week and Mr McCormack said the government would not rule them out.
While witnesses said hundreds of civilians died in the incident, the government put the figure at 187 people.
Since the event, the BBC and many other international media organisations have not been able to operate freely in Uzbekistan.
The BBC's Natalia Antelava on the Uzbek-Kyrgyz border says there will be no public mourning and no official memorial service for the civilians in Uzbekistan.
She says many refugees on the border still do not know what happened to their relatives who were at the square in Andijan on the night of 13 May 2005.
A small protest in Tashkent on Friday was broken up
Survivors talk about mass graves and mass arrests but none of it is possible to confirm independently.
Jenny Norton of BBC News says trouble had been brewing in Andijan for weeks before last year's incident.
A group of local businessmen had gone on trial accused of being Islamic extremists.
Their relatives and supporters had defied the authorities to maintain a silent protest outside the courtroom.
The night before the verdict was due a group of armed men attacked the town jail.
They freed all the inmates - including the businessmen - and went on to occupy the town hall.
The following morning people came to the main square to find out what was happening.
At about 1700 the troops moved in, sealed off the square and opened fire on the crowd with machine guns. The shooting went on for more than an hour.
One year on, protests are planned in London, Belgium, Egypt and Moscow among other places.
Eight people who tried to mount a demonstration in the Uzbek capital, Tashkent, on Friday were stopped by security officials.