BBC's Lindsay Marnoch: The report cites the action at Waco

In a report to the United Nations Committee against Torture, the State Department said areas of concern included police abuse, death of prisoners in custody, prison overcrowding and a lack of adequate training for police and prison guards.

Some 18 examples were cited of abuses committed by US police and prison officials since 1991.

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"Torture does not occur in the United States except in aberrational circumstances and never as a matter of policy," the report said.

"No government, however, can claim a perfect record ... Abuses occur despite the best precautions and the strictest prohibitions."

The well-publicised beating of black motorist Rodney King by four Los Angeles police officers in 1991, and the recent harsh treatment of Abner Louima, a Haitian immigrant, by New York City police officers were among the incidents cited.

Waco siege

Others were excessive use of force by federal authorities against the Branch Davidian religious sect in Waco, Texas, in 1993 and the shooting of a white supremacist in Ruby Ridge, Idaho, in 1992.

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But the report, the first the US has sent to comply with the UN Convention against Torture, stressed that torture was prohibited by law throughout the US, and that no official was authorised to commit or sanction torture.

It said perpetrators were prosecuted and victims entitled to compensation.

It also defended the legality and use of the death penalty.

Executions

"The United States considers the issue of capital punishment to be outside of the scope of its reporting obligations under this Convention," the report said.

It noted that voters in a majority of states had chosen to have capital punishment as an option in sentencing severe crimes.

But the World Organisation Against Torture said incidents of abuses in the United States were "surprising and alarming in scope" and accused Washington of not doing enough to prevent them.