Former Khmer Rouge prison chief Duch asked Cambodia's UN-backed war crimes court on Friday to acquit and release him on the final day of arguments in his trial.

Following a query by shocked judges, Duch's Cambodian lawyer Kar Savuth confirmed that Duch was asking to be acquitted on the grounds that he was not a senior member of the Khmer Rouge hierarchy.

International prosecutors earlier this week asked judges to impose a jail sentence of 40 years on Duch - a former maths teacher and born again Christian - for his role in the brutal 1975-1979 communist regime.