The ongoing feud between Sinead O'Connor and Miley Cyrus is heating up as O'Connor is demanding an apology in her fourth open letter to the 20-year-old pop star.

This back and forth feud between the two singers started when Cyrus credited O'Connor's "Nothing Compares To You" as an inspiration for her "Wrecking Ball" video.

The Daily News reports that O'Conner took to her website to post an open letter to Cyrus. in the letter she explains how Cyrus is being "pimped" by the music industry.

"They will prostitute you for all you are worth, and cleverly make you think it’s what YOU wanted and when you end up in rehab as a result of being prostituted, 'they' will be sunning themselves on their yachts in Antigua, which they bought by selling your body and you will find yourself very alone," O'Connor said.

"I am extremely concerned for you that those around you have led you to believe, or encouraged you in your own belief, that it is in any way 'cool' to be naked and licking sledgehammers in your videos," she continued.

Cyrus responded to the letter via twitter.

A short while after, O'Connor posts a second letter to Cyrus on her Facebook page.

In the letter, she criticizes Cyrus for mocking mental illness, which she feels very serious about, and that it should not made fun of.

"You have posted today tweets of mine which are two years old, which were posted by me when I was unwell and seeking help so as to make them look like they are recent," O'Connor said. "In doing so you mock myself and Amanda Bynes for having suffered with mental health issues and for having sought help."

"I hope that you will apologise to Amanda Bynes and to any person who has been wounded by your mockery of those who have suffered," she added.

Cyrus responded that same day on Twitter.

The next day, O'Connor wrote a third letter to Cyrus on her Facebook page, telling her to apologize and that she would bring about legal action for her mockery of mental illness, stating that it affected her chances of getting work.

"What you did yesterday was designed to damage me and my career and has caused me enormous distress and harassment and has potential to damage my career, since you deliberately gave the impression those tweets of mine were not two years old but reflect my current condition," O'Connor said. "If you cannot apologize I will have no choice but to bring legal proceedings against you since it is extremely hard to be given work when people think one is suffering from mental illness."

MTV reports that on Monday, Oct. 7, in an interview with Today, Cyrus explained that O'Connor's response came out of nowhere.

"I don't know how someone can start a fight with somebody that's saying, 'Hey I really respect you and I really love what you did.' 'You know what? You suck!' And that was kind of crazy," Cyrus said. "But, like I said, I'm a big fan of hers and so it doesn't really matter... It's all good."

O'Connor recently posted a fourth letter to Cyrus on her website, still asking for an apology.

"I would very much like you please to apologise to myself and Amanda Bynes for having perpetuated abuse of both of us on the grounds that Amanda has had ‘mental health issues’ and that I experienced suicidal compulsion and was open about seeking help in order to save my life," O'Connor said.

"This should also involve an apology to all sufferers of mental health difficulties and all those who have had experience of suicidal feelings or who have been affected by suicide," she added.

O'Connor also addressed the feud that they're having.

"I have no interest in the 'feud' which media want. There is no 'feud' as far as I am concerned. What there is however.. Is a lot of very serious harm caused to myself and my children and probably to Amanda, and DEFINATELY to silent sufferers of your own age who may look up to you," she said.

She closed the letter, once again asking Cyrus to own up to responsibility to the people in which she may have caused harm.

"Please do the right thing. You will actually save lives by doing so," she said. "There are people who will NOT die tonight, if you are brave enough to state that there is nothing whatsoever wrong with any person seeking publicly or privately, help, in order to stay alive. And that there are no circumstances under which it is acceptable for anyone to use mental illness as a stick with which to beat people."

Cyrus's new album Bangerz released in stores and on iTunes today.

Photo Courtesy of MTV