Asia Argento, the #MeToo activist immersed in conflicting allegations of rape and underage sex, has demanded that her former fellow activist, Rose McGowan, retract "horrendous lies" about her or else face a defamation lawsuit.

In an early morning tweet prefaced with "genuine regret", Argento accused McGowan of libel and demanded an apology.

There was no immediate response from McGowan, at least on Twitter. Her publicist did not immediately return a message.

The tweet represents Argento's response - now that she has a new lawyer - to a long statement McGowan issued last month in which she took the side of former child actor Jimmy Bennett, who says he and Argento had sex when he was 17 and she was 37 in 2013.