The lawyer, who has not been named, told the Irish Independent that the fraud involved someone posing as a solicitor from “Rowan and Walsh Law”, a fake law firm that purported to be based in Dublin.

The Legal Services Regulatory Authority (LSRA) issued a warning about “Rowan and Walsh Law” last month, making clear that it is not registered with the Law Society of Ireland.

The victim, in New Jersey, said he was convinced to hand over more than $800,000 (around €765,000) to someone he met on a dating website but had never met in person.

This person, who he believed to be a woman living in Texas, told him that she was the owner of valuable diamonds which were held in Ireland and were at risk of passing into the ownership of the State.

He was offered a share of the proceeds if he helped to cover the costs of importing and selling the diamonds, and was persuaded after seeing documents which “appeared authentic”.

After he realised that “Rowan and Walsh Law” was not a real firm, the woman vanished and his money was gone.

Dr Brian Doherty, chief executive of the LSRA, told the Irish Independent: “The LSRA takes such matters very seriously and we will take every action within our powers to assist those who are targeted by these kinds of sophisticated fraudsters.

“We have assisted the victim in every way possible and advised him to report this matter to An Garda Síochána and the FBI without delay.

“Unfortunately, by the time these illegal activities came to our attention, the victim had already transferred substantial sums of money to the criminals.”