Updated at 8.05pm with Casa reaction
A secret document released by MEP David Casa has been re-typed, and contains "noted several discrepancies, omissions and inaccurate reproductions of text", the FIAU said on Monday evening, claiming it was not one of the unit's reports and nor is it a faithful reproduction of any FIAU document.
The FIAU also said that it would demand that action was taken against Mr Casa, which the MEP said would not deter his quest for justice.
The 109-page FIAU report published on Monday afternoon gives details of transactions relating to Tourism Minister Konrad Mizzi and payments made to 17 Black - which conclude that there was enough information to merit an investigation into possible money-laundering.
The Prime Minister’s chief of staff Keith Schembri and Dr Mizzi had listed 17 Black as one of two so-called “target clients”, which were set to pay in millions to their once-secret Panama companies.
Read: Casa publishes FIAU report showing €1.3m 17 Black transactions
"Mr Casa refers to this document as an FIAU report, notwithstanding that the FIAU has repeatedly confirmed that this document contains intelligence and other sensitive information which, at the time it was illegally leaked from the FIAU, was still work in progress," it said.
The agency said that the information was secret and illegally obtained, and that it placed the safety of a number of FIAU officials "at serious risk" - apart from the impact it would have on its credibility and therefore ability to obtain and exchange intelligence from its international counterparts.
It said that the publication could also hinder any possible ongoing police investigations but gave no confirmation as to whether there were any.
With regards to Mr Casa's source, the FIAU said the MEP has therefore "not only handled stolen sensitive information, but appears to be protecting persons who have carried out criminal acts, and is using information which the FIAU has obtained for his own political mileage.
"Mr Casa’s position as an MEP does not place him above the law and the FIAU will demand that action be taken," it said.
Mr Casa said later that it was "disgraceful" to be threatened with arrest by the FIAU.
"Instead of acting on the conclusions of the mentioned report - and take action against Konrad Mizzi - the authorities in Malta have been reduced to government mouthpieces. I will not stop fighting for justice - irrespective of the threats I receive. The public deserves the whole truth. I will continue to do my utmost to ensure that those who are involved in corruption and money laundering are brought to justice," he said.