The US said today it was "deeply disturbed" by reports Uzbek authorities fired on unarmed demonstrators last week as they suppressed a rebellion in the former Soviet state that is a strategic ally of Washington.
Secretary of State Condoleezza Rice also called for political reform in the Central Asian country, where autocratic President Islam Karimov has ruled since Soviet times and the United States has a major air base supporting Afghan operations.
"We are deeply disturbed by the reports that the Uzbek authorities fired on demonstrators," State Department spokesman Richard Boucher told reporters.
"We certainly condemn the indiscriminate use of force against unarmed civilians and deeply regret any loss of life."
The comments were the strongest from the United States since a blood bath in the town of Andizhan on Friday when troops killed 500 protesters, according to some estimates.
Ms Rice, who has sought to promote democracy in former Soviet states, said Uzbekistan had a political system that was "too closed."
"We have been encouraging the Karimov government to make reforms, to make the system more open, to make it possible for people to have a political life," said Ms Rice, who spoke to reporters as she flew home after a trip to Iraq.
Her remarks followed criticism from the European Union, which said the protests came as a result of the government's failure to respect human rights and the rule of law. Karimov blamed Friday's rebellion on Islamic extremists, whom he also fingered for a string of bomb attacks last year in the country.
Few political experts expect the uprising in Andizhan to emulate the success of the March rebellion in neighbouring Kyrgyzstan, which led to the overthrow of its president.
In balancing the US criticism, Mr Boucher condemned an attack on the day of the protests on the town's prison apparently by armed rebels who the United States fears freed militants.
"There's nothing that justifies acts of violence or terrorism, and we're very concerned at reports of either the release or the escape of the Islamic Movement of Uzbekistan members," he said.
The ex-Soviet republic, where only state-sponsored Islam is tolerated, has been criticized by human rights groups for jailing dissident Muslims and using torture. They say there are at least 6,000 religious and political prisoners there.