WASHINGTON (REUTERS) - A US soldier charged with slaying 16 civilians in Afghanistan will undergo a sanity review set to begin next week to determine his mental state during the killings and his ability to stand trial, a military official said on Wednesday.

Prosecutors are seeking the death penalty against Army Staff Sergeant Robert Bales, and his defence attorneys have indicated they are preparing a possible mental health defence.

The decorated veteran of four combat tours in Iraq and Afghanistan is accused of killing 16 Afghan villagers in cold blood during two rampages through their family compounds in Kandahar province in March 2012.

The slayings have further eroded strained US-Afghan relations after more than a decade of conflict in that country.

Bales will receive a court-ordered sanity board review beginning on Sunday, with the proceedings potentially lasting several days, said Lieutenant Colonel Gary Dangerfield, an Army spokesman at Joint Base Lewis-McChord in Washington state where the Bales case is being heard.

Defence attorney Emma Scanlan said in January that Bales would participate in a review of his mental state, but wanted him to be examined by a neuropsychologist with expertise in traumatic brain injuries. She also sought for defence attorneys to be present at the examination.

It was unclear if those requests would be honoured at the sanity board review.

Dangerfield said Bales would appear before the sanity board at an undisclosed location.

Attorneys for Bales could not be reached for comment late on Wednesday.