Madonna and her daughter Lourdes
Madonna and her daughter Lourdes Leon arrive at the premiere of the film "Nine" in New York. Reuters

Madonna's 15-year-old daughter Lourdes Leon was photographed smoking a cigarette in New York and material mom is not happy about it. While the legal age for smoking in America is 18 years, Leon was caught breaking the law in New York last month.

The 53-year-old singer finally spoke about her daughter's controversial smoking picture almost a month later. When a photograph of Leon smoking surfaced online, Madonna was not pleased.

The singer, in an interview with NBC's Rock Center, admitted that she wasn't very happy when she came to know about her teenage daughter's controversial picture. Madonna believes that she's a tough mom, but not as tough as she would like to be.

[I] wasn't very happy, she told Rock Center's Harry Smith. Honestly, I don't think I'm as tough as I should be. I think I need to be maybe tougher, but it's hard, though. It's hard. Every day is a negotiation.

Although the single mother of four believes that she needs to be tougher with her kids, she also denied that Leon could have picked up the behavior from her.

Cigarette smoking I'm not very fond of -- for anyone. I don't approve of anyone smoking cigarettes, most of all my daughter, she said.

When Smith pointed out her smoking a cigarette in her newest music video, Girl Gone Wild, Madge got defensive and said it's not quite a case of do as I say, not as I do.

I don't smoke, Madonna clarified. That cigarette was just an accessory...there's a difference. [Lourdes] smoked that cigarette before I did that video. She didn't get that from me.

While Madonna said she had warned her daughter to watch her hemlines, she also admitted that it has not been possible to always enforce the kind of discipline that she actually wants.

To be a single mother of four and to work as much as I do, to live my life in kind of a metaphorical fishbowl, it's pretty challenging, she said. But so far I've survived with sanity and humor intact.