MEXICO CITY (REUTERS) - Videos showing Mexico City subway riders reacting to close-ups of men's buttocks and subway seats with moulded penises were part of a bold advertising campaign launched recently by UN Women, an arm of the United Nations.

The videos have been on YouTube since March 20, but it was only this week that UN Women issued a press release taking responsibility for the initiative.

At a press conference on Thursday (March 30), the organisation said it would show the videos on 12 subway lines in Mexico City over the next three weeks.

The first video, called Seat Experiment, showed subway riders' reactions to a seat moulded in the shape of a nude male body with a prominent penis. Lots of men who tried to sit on the seats were surprised or uncomfortable.

"It's unpleasant sitting here, but it's nothing compared to the sexual abuse women experience on their commute every day," reads a sign on the floor below the seat.

Nearly six million people take the Mexico City subway each day and women are molested on a regular basis. Trains have had designated women-only subway cars for years and beginning last year, men who use them have been subjected to fines.

In the second video in the campaign, Screen Experiment, men waiting for the subway see their buttocks projected onto subway television monitors. Many women smile as some of the men cover up their backsides in humiliation.

The campaign drew angry reactions from some men on YouTube and Twitter, who felt they were being stigmatised as rapists and criminals.

According to UN Women, nine of every 10 women in Mexico City, one of the world's most populous metropolises, have been subjected to some type of sexual abuse riding the subway.