According to local reports, the firm said: “We featured him for his hair, not terrorism.”
In the 9/11 Commission report, Khalid Sheikh Mohammed is described as "the principal architect of the 9/11 attacks."
He is currently detained in Guantanamo Bay after being captured by the US military in 2003 in Pakistan.
"We didn't know that he was a terrorist," she said. "This image is in popular use in Turkish memes on the internet. The guy is quite hairy, so we thought his body was a good fit for our ad.
"We didn't want to imply anything political. We didn't know that it could become an international story. I repeat: We featured him for his hair, not terrorism."