UPDATE 1-Top Vatican cardinal accuses papal critic of "calumny and defamation"

A top Vatican official on Sunday issued a scathing open letter accusing an archbishop who launched an unprecedented attack on Pope Francis of mounting a "political frame job devoid of the real foundation".

Cardinal Marc Ouellet said in the detailed, three-page letter that calls by Archbishop Carlo Maria Vigano for the pope to resign because he had allegedly covered up sexual misconduct by a senior American churchman were "calumny and defamation".

Ouellet, who heads the Vatican's powerful Congregation for Bishops, issued the letter in response to a bombshell statement on Aug. 26 by Vigano in which he accused a long list of current and past Vatican and U.S. Church officials of covering up for Theodore McCarrick, 88, the former archbishop of Washington, D.C., and called on the pope to resign.

Vigano said the pope knew for years about sexual misconduct by McCarrick with adult male seminarians but did nothing about it.

Ouellet's letter was a point-by-point rebuttal of Vigano's statements. He said Vigano, who is in hiding and has issued his accusations exclusively through conservative Catholic media which are traditionally antagonistic towards the pope, had let himself "be convinced of this monstrous accusation".

Ouellet, a Canadian, said: "Come out of hiding, repent for your revolt and return to better feelings towards the Holy Father instead of worsening hostility against him".

(With inputs from agencies.)