A US soldier who blew the whistle on his comrades over possible drug use and the deaths of three civilians in southern Afghanistan suffered a severe beating in retaliation, officials said Tuesday.

The soldier was beaten after telling authorities about illicit drugs and then, while recovering in hospital, recounted his comrades' alleged role in the deaths of three Afghan civilians, said two officials, who spoke on condition of anonymity.

The soldier was "beaten within an inch of his life," one of the officials told AFP.

US Army authorities last week said they were investigating the "unlawful" deaths of three Afghans as well as allegations of illegal drug use, assault and conspiracy.

Defense officials said the investigation focuses on at least 10 members from the 2nd Infantry Division's Fifth Stryker Brigade, which deployed to Kandahar province in the summer of 2009 and initially suffered heavy casualties, officials said.

One soldier has been placed in detention in the case and authorities said last week the probe was launched this month after receiving "credible information" from the soldiers' unit earlier this month.

The Afghan civilians were found dead at some point between January and March, officials said.

The US Army Criminal Investigation Command declined to comment on the details of the case.

The allegations come at a sensitive moment in Kandahar, as the US military tries to push back the Taliban from its spiritual heartland -- a pivotal operation that hinges on winning the trust of local Afghans.

US officers say the outcome of the war could be riding on the result of operations in and around Kandahar.

Civilian casualties in the nearly nine-year conflict in Afghanistan are deeply controversial and a source of tension between Afghan President Hamid Karzai and the US-led foreign military.