The unlikely war of words between Miley Cyrus and Sinead O'Connor has continued apace, with the Irish singer threatening the controversial young star with legal action.

The argument started when Cyrus compared her "Wrecking Ball" video to O'Connor's "Nothing Compares 2 U" clip in an interview with Rolling Stone magazine.

After getting calls from reporters begging for her thoughts on the comparison, O'Connor took to her website to post an open letter to Cyrus, warning her that her sexually provocative image showed she was being exploited by the music industry.

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Cyrus took to Twitter, comparing O'Connor to the actress Amanda Bynes, the troubled star who was reportedly recently moved to a private treatment facility. In the tweet there was a link to a screen-grab of tweets from O'Connor, in which the older star was asking for help with her bipolar disorder.

In addition, Cyrus posted a picture of O'Connor ripping up an image of Pope John Paul II on Saturday Night Live.

She then wrote: "Sinead. I don't have time to write you an open letter cause I'm hosting & performing on SNL this week. So if you'd like to meet up and talk lemme know in your next letter."

In her second and third letters to Cyrus, O'Connor was predictably furious.

"Taking me on is even more f****** stupid than behaving like a prostitute and calling it feminism," she wrote.

"Ms Cyrus has today posted tweets of mine which are two years old and which were sent when I was ill and seeking medical help.

"She has done this in an attempt to deliberately cause me harm and hurt. I wish to confirm that I am quite well and kindly request people cease emailing me in the mistaken belief these are recent tweets."

Threatening legal action, she wrote: "Ms Cyrus' lawyers will be contacted by mine regarding this matter."

O'Connor said she had no interest in meeting up with Cyrus, but added: "You can take five minutes today between g-string f****** changes to publicly apologise and remove your abusive tweets."