The former Vatican ambassador who accused three popes and their advisers of covering up for a disgraced American ex-cardinal has denounced Pope Francis' refusal to directly respond to his claims and challenged the Vatican to say what it knows about the scandal.

Cardinal Carlo Maria Vigano penned a new missive a month after his initial 11-page bombshell sent shockwaves through the Catholic Church. It was uploaded to a document-sharing site late Thursday.

In the document, Vigano denounced the official Vatican silence about his claims and accused Francis of mounting a campaign of "subtle slander" against him. He urged the head of the Vatican bishops office to speak out, saying he has all the documentation needed to prove years of cover-up of allegations of sexual misconduct of ex-Cardinal Theodore McCarrick.