Nun in disguise, stabs woman in crime thriller

Looking for a film or TV series/serial, which had a crime/thriller/espionage theme. A scene I remember (maybe towards the end) was when a woman was walking down the street and a woman from the bad guys’ team was coming the other way, disguised as a nun, and stabbed and killed the girl. The bacidrop for the film might have been european, maybe Italian, or Greek or perhaps North African. It was on British TV in the late 70’s, so it was a film/program from maybe late 50’s/60’s/ (or maybe even early 70’s, but I think earlier - fasion was 40’s-60’s I think, and I think it was in colour). Any ideas?