The Vatican has denied that Pope Francis failed to speak out against human rights abuses during military rule in his native Argentina.

"There has never been a credible, concrete accusation against him," said Vatican spokesman Federico Lombardi, adding he had never been charged.

The spokesman blamed the accusations on "anti-clerical left-wing elements that are used to attack the Church".

Jorge Bergoglio, now Pope Francis, led Argentina's Jesuits under the junta.

Correspondents say that like other Latin American churchmen of the time, he had to contend, on the one hand, with a repressive right-wing regime and, on the other, a wing of his Church leaning towards political activism on the left.

One allegation concerns the abduction in 1976 of two Jesuits by Argentina's military government, suspicious of their work among slum-dwellers.

As the priests' provincial superior at the time, Jorge Bergoglio was accused by some of having failed to shield them from arrest - a charge his office flatly denied.

Judges investigating the arrest and torture of the two men - who were freed after five months - questioned Cardinal Bergoglio as a witness in 2010.

The new Pope's official biographer, Sergio Rubin, argues that the Jesuit leader "took extraordinary, behind-the-scenes action to save them".

Another accusation levelled against him from the Dirty War era is that he failed to follow up a request to help find the baby of a woman kidnapped when five months' pregnant pregnant and killed in 1977. It is believed the baby was illegally adopted.

The cardinal testified in 2010 that he had not known about baby thefts until well after the junta fell - a claim relatives dispute.