Miley Cyrus has hit back at Sinead O'Connor in an escalating online war of words and invited her to a face-to-face chat to air their differences.
The offer of a meeting came after the Irish singer said she was "extremely concerned" about the US singer's Wrecking Ball music video and warned her not to be exploited by the music business, in an open letter on her website.
But Cyrus, 20, responded by mocked the Nothing Compares 2 U singer in a series of Twitter posts, likening her to troubled actress Amanda Bynes, who is undergoing psychiatric treatment.
She also reminded her followers of O'Connor's past by posting a picture of her tearing up a photo of the then pope, as well as a screenshot of her older tweets from 2012, when she had asked her followers to recommend a psychiatrist.
Cyrus tweeted: "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."
O'Connor went on to write a further open letter, and suggested she would sue the Hannah Montana star - who has recently featured in a number of provocative and scantily clad public performances - if she does not apologise publicly or remove the tweets.
"I have no interest whatsoever in meeting you. You had plenty of time yesterday to abuse Amanda Bynes ... an entirely innocent party ... and myself.. who also did nothing to deserve your abuse," the 46-year-old said.
"If you do not apologise 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. I have no interest in or desire to cause you trouble..."
She added: "I can't imagine your parents being at all proud of what you did yesterday."
Cyrus appears naked in her Wrecking Ball video and performed a raunchy routine at an MTV awards ceremony in the US. She has also posed in a tiny leotard for saucy photographer Terry Richardson.