The unrest on Monday night came as police and troops stepped up patrols in the city's streets.
Last Friday, witnesses said, soldiers tried to disperse an anti-government rally in Andijan by firing into the crowd.
The unrest started when demonstrations over the trial of 23 local businessmen, accused of membership in an outlawed Islamist group, boiled over.
But President Islam Karimov's government has long been accused of gross human right abuses and observers say the Uzbek authorities purge Muslims who do not follow state-sanctioned Islam.
US-based watchdog Human Rights Watch estimates that this religious persecution has resulted in the unfair arrest and incarceration of around 7000 people.
The Uzbek government has banned the call to prayer, and forbids any discussion of an Islamic state or Islamic law. Attendance at a mosque can result in arrest.
Last Friday, soldiers fired into
a crowd to disperse them
There is no independent media in Uzbekistan and all state-run media is subject to heavy censorship.
The Uzbek government justifies this campaign by saying that it needs to act against terrorism and places its actions in the context of the war against terrorism.
Uzbekistan is also an ally of Washington and the US army has bases in the country, from which attacks were launched on neighbouring Afghanistan in October 2001.
Since 1992, the US has given Karimov's government more than $1 billion in aid, some of which was allocated to the Uzbek police and intelligence services.
In one incident, a forensic report commissioned by the British Embassy in Afghanistan concluded that two prisoners had been boiled to death.
Torture is commonplace as is extra-judicial punishment and scores of Uzbeks have died in prison. Rape is also used as a tool of torture
Washington said on Monday that it was "deeply disturbed" by reports that Uzbek security forces fired on demonstrators during unrest, which is said to have left hundreds dead.
Boucher: Violence cannot lead
to long-term stability
The State Department urged Uzbekistan's government, one of the strongest US allies in the region, to show restraint in dealing with the unrest.
"We are deeply disturbed by the reports that the Uzbek authorities fired on demonstrators last Friday. We certainly condemn the indiscriminate use of force against unarmed civilians and deeply regret any loss of life," State Department spokesman Richard Boucher told a news briefing.
"We had urged and continue to urge the Uzbek government to exercise restraint, stressing that violence cannot lead to long-term stability. And we've made that point with senior Uzbek authorities in Washington and Tashkent."
But Boucher also condemned armed attacks by civilians on the prison and other civilian facilities in Andijan. "It is the kind of violence that we cannot countenance in any way," said the US spokesman.
"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."
Rice urges calm
Meanwhile, US Secretary of State Condoleezza Rice on Monday urged Uzbekistan to adopt political reforms to head off future unrest.
Rice said Uzbekistan should have
a more open political system
Rice said US officials were till trying to sort out what happened in Andijan and the events behind the killing of so many protesters.
"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," Rice said.
"This is a country that needs, in a sense, pressure valves that come from a more open political system," Rice told reporters on the plane taking her home from a surprise visit to Iraq.