By Andrew North
BBC correspondent in Kabul
The actions of US military and intelligence units in Afghanistan have been heavily criticised in a new report by an international human rights group.
The rights advocates oppose the use of helicopter gunships
US-based Human Rights Watch accuses US personnel of using excessive force, carrying out arbitrary detentions and mistreating people in custody.
Washington keeps about 9,000 troops on Afghan soil, involved primarily in fighting the Taleban and al-Qaeda.
But the human rights body says many US actions violate international law.
The report is damning. Entitled Enduring Freedom - Abuses by US Forces in Afghanistan, it focuses on the American system of detaining people at bases across the country, which it describes as "almost entirely outside the rule of law".
According to Human Rights Watch, at least 1,000 Afghans and other nationals have been taken into custody since 2002.
These arrests have often been accompanied by excessive or indiscriminate force, it says, leading to death and injury to innocent civilians.
Helicopter gunships have been used to fire on residential areas, when US troops were facing no opposition.
Once in custody in places like Bagram airbase north of Kabul, mistreatment is common, the human rights group says - detainees are frequently subjected to sleep deprivation, extremes of temperature and in some cases beatings.
Two people have died in US detention in Afghanistan, and both cases have been ruled as homicide.
Human Rights Watch says these incidents have still not been adequately explained by the Pentagon. The report's writer fears "appropriate criminal and disciplinary action may never take place".
The group points out that the US government has condemned as torture in other countries many of the methods its forces have allegedly employed in Afghanistan when interrogating detainees.
Such behaviour, it concludes, sends a message that "the US operates on a set of double standards", which also undermines support for its war on terror.
Afghan human rights campaigners have also voiced concerns about American tactics.
Asked about the Human Rights Watch allegations, Lt Col Bryan Hilferty, the US military spokesman in Afghanistan, said: "We've seen the report, we are taking the allegations seriously."
But he continued: "We feel it shows a lack of understanding of the laws of war and of the environment we are facing in Afghanistan.
"They say we should be using police procedures when we carry out arrests, but this is a combat zone."
The report may cause some discomfort for the government of President Hamid Karzai.
Although it has expressed concern about some US tactics - particularly over incidents where innocent civilians have been killed - it has been reluctant to criticise the American military publicly.
It wants US troops to stay, a position supported by many Afghans.
But Human Rights Watch says President Karzai should put more pressure on the US government to uphold humanitarian and human rights laws in Afghanistan.