An Afghan soldier “executed” a prisoner on a British base in Helmand province, Ministry of Defence documents disclose.
It is understood that UK troops did not directly witness the killing but were close by at the time.
British military investigators carried out an inquiry into the shooting of the detainee on a small UK-controlled patrol base in Musa Qala in March.
It is believed that the Afghan soldier who carried out the killing was handed over to the local authorities, although it is not clear what happened to him.
Details of the incident emerged in a training manual for troops deploying to Afghanistan released by the MoD as part of the Baha Mousa public inquiry into abuse of Iraqi prisoners.
The document, which has a “restricted” security classification, outlines how UK forces should treat detainees captured during operations.
Referring to the current situation in Afghanistan, it says: “Allegations of detainee abuse by ANSF (Afghan National Security Forces) and Isaf (the Nato-led International Security Assistance Force) troops continue – some reported to ICRC (the International Commission of the Red Cross).
“Alleged that during Mar 10 a [sic] ANA (Afghan National Army) soldier ’executed’ a detainee who was in their custody within a British-controlled PB (patrol base).”
Campaigners have raised concerns about the treatment of Afghan prisoners captured by British forces.
Musa Qala was under control of soldiers from the Household Cavalry at the time of the killing of the detainee in March. The district was handed over to the US Marines shortly afterwards.
A massive programme to expand the Afghan security forces – the goal is that their numbers should grow from fewer than 200,000 at the start of this year to 300,000 by the end of 2011 – is under way.
But concerns have been expressed about the quality and allegiance of some recruits.
In July an Afghan soldier murdered three British troops from 1st Battalion The Royal Gurkha Rifles at a base near Helmand’s capital, Lashkar Gah.