MADRID (Reuters) - Outgoing Defense Secretary Donald Rumsfeld authorized the mistreatment of detainees at Abu Ghraib prison in Iraq, the prison's former U.S. commander said in an interview on Saturday.

Former U.S. Army Brigadier General Janis Karpinski told Spain's El Pais newspaper she had seen a letter apparently signed by Rumsfeld which allowed civilian contractors to use techniques such as sleep deprivation during interrogation.

Karpinski, who ran the prison until early 2004, said she saw a memorandum signed by Rumsfeld detailing the use of harsh interrogation methods.

"The handwritten signature was above his printed name and in the same handwriting in the margin was written: "Make sure this is accomplished"," she told Saturday's El Pais.