The Vatican has taken the unprecedented decision to release confidential files about an abuse case in the US in an attempt to defend itself against accusations of a cover-up.

The documents are a response to a high-profile lawsuit revolving around the sovereign immunity status of the Vatican in relation to the case of a now-deceased Irish-born priest, Father Andrew Ronan, in the US state of Oregon.

The unnamed plaintiff said he was abused by Ronan in 1965 when he was 17.

The plaintiff, referred to as John Doe in court documents, alleged that ‘the Holy See was vicariously liable for Ronan's abuse of Doe and... negligent in its retention and supervision of Ronan and in failing to warn of his propensities.’

But the Vatican said it had not been informed about the case until 1966, when Ronan himself asked to be defrocked after the alleged abuse.

It published letters and official documents on Vatican radio's website.

While the documents do not reveal a direct link to the Vatican, they do show that senior clergy had suspicions about Ronan for years before 1965.

The Vatican's US lawyer Jeffrey S Lena said the files demonstrate that the ‘long-standing accusations against the Holy See are false.’

‘The Holy See was not involved in Ronan's transfers, including the transfer to Portland, and had no prior knowledge that Ronan posed a danger to minors,’ he said.

‘Instead, the documents confirm that the Servite Order first informed the Holy See of Ronan's misconduct when Ronan petitioned for laicisation in February 1966 - after the plaintiffs abuse,’ he added.