The Vatican has come under fire for its failure to respond to a shocking grand jury report which alleged decades of sexual abuse by Catholic priests in Pennsylvania.

The Holy See's press office declined to comment on the report but critics said the Pope's office should respond to the claims against some 301 clergymen over a period of more than 70 years.

One Catholic writer said Pope Francis's response to the claims had been 'disappointing' while an academic called the Vatican's silence 'disturbing', CNN reported.

At least 1,000 children were molested and assaulted by 'predator priests' who used Catholic rituals and symbols of the faith to commit their horrifying abuse, the grand jury found.

The Holy See's press office declined to comment on the report but critics said Pope Francis (pictured) should respond to claims against some 301 clergymen over a more than 70 years

Pennsylvania theology academic Massimo Faggioli said: 'The silence from the Vatican is disturbing.

'I don't think the Pope necessarily has to say something today. He needs time to understand the situation... but someone from the Vatican should say something.'

Catholic magazine editor Matthew Schmitz said on Twitter: 'Francis has at times been unfairly attacked for his handling of sex abuse but his record is still disappointing.

'He needs to act now by authorizing a full investigation of the American hierarchy.'

A papal legate should conduct formal interviews and make recommendations to the Pope about 'appropriate penalties', he said.

Priests across Pennsylvania used religious rituals and the threat of eternity in hell to groom, molest and rape children, a grand jury found, in what the state's top prosecutor Josh Shapiro called the 'weaponization of faith.'

In a letter to the Pope, Shapiro said the report had found a 'systemic cover-up' of the sexual abuse by leaders of the Catholic church.

He called on the Pope to urge church leaders to 'abandon their destructive efforts to silence the survivors' and 'follow the path of truth'.

One priest tied up a victim with rope in the confessional in a 'praying position,' the grand jury wrote. When the victim refused to perform sex, the angered priest used a 7-inch crucifix to sexually assault him, the report said.

At least 1,000 children were molested and assaulted by 'predator priests', the grand jury found. Pictured: The state's Attorney General Josh Shapiro at a press conference on Tuesday

One priest rinsed a boy's mouth with holy water after abusing him while another priest allegedly told a boy he was fondling that it was OK because he was 'an instrument of God.'

In another church, a priest told a boy who confided he had been gang-raped as a 7-year-old that he had to provide sex to get to heaven.

At a parish rectory, the report said, four of the priests made a boy strip and pose as Jesus on the cross while they took photos.

Only two of the priests have been charged with crimes as a result of the grand jury investigation, though a number were prosecuted in years past. Over 100 have died, and many others have retired.

The Pennsylvania grand jury said that in almost every case there, the statute of limitations for bringing criminal charges has run out.

Church leaders say most of the offenses occurred some time in the past and note that major reforms were adopted starting in 2002 to safeguard children.