The sentencing hearing for a US soldier who killed 16 Afghan civilians last year has begun, as he prepares to face survivors and relatives of his victims.

Staff Sgt Robert Bales, 39, admitted to the March 2012 massacre in June as part of an agreement to avoid execution.

On the night of the killings he was serving his fourth tour of duty and had been drinking alcohol and using Valium.

The BBC's Alastair Leithead reports.