Christy Kinahan and sons may have already been charged in secret US court proceedings

Brian O'Toole, a senior fellow the Atlantic Council think-tank, told the Sunday World that sanctioned individuals can also be the subject of a sealed indictment.

"It would not be unusual for sanctions to take place while a sealed indictment remains sealed, that does happen from time to time."

Mr O'Toole, who served as a senior adviser in the US Treasury's Office of Foreign Assets Control and as an illicit finance analyst at the CIA, also said the reward for the Kinahans is "a big number".

"It's a pretty big a number for State [Department]. Usually when you see these things come out it's a couple of hundred thousand or low millions for significant Latin American traffickers.

"Five million for each of them is quite a lot."

The same $5million bounty has been offered for information on two of Joaquim 'El Chapo' Guzman's sons, who are believed to have taken over the running of his multi-billion-dollar Sinaloa Cartel in Mexico.

It is also unusual for a European criminal gang to be placed on the list, according to O'Toole, with most sanctions against south and central American drug traffickers.

"There is more direct impact on the US from those western hemisphere gangs. It is uncommon for a European crime group to end up on the list."

"The last European gang I can remember landing on the sanctions list was probably some of the Russian groups in the 2012-2014 time-frame."

The Kinahans join arms dealers for the Myanmar military junta, people working on missile programmes in North Korea and Iran, as well as all 328 members of the Russian State Dumas (parliament) who voted for the war against Ukraine.

The US Treasury sanctions list from just the last few months reads like a Who's-Who of the global black market - and those named are considered a serious threat to society.

On the sanctions list this year there is the largest diamond mining firm targeted with links to the Kremlin, as well the world's largest darknet marketplace and an African police force accused of human rights abuses.

It is an indication that the criminal organisation with the Kinahans at its heart had become too big to ignore.

A month before the Irish cartel were sanctioned, the alleged leader of the Los Huistas cartel, which controls a strategic border area in Guatemala with Mexico, was also listed.

Authorities in the US have also brought charges against Eugenio Dario Molina-Lopez, also known as "Don Dario," including conspiracy to distribute cocaine.

A $10million reward has been offered for his capture.

According to US Treasury department, Los Huistas smuggles cocaine, methamphetamine and heroin to the US using the Sinaloa Cartel and the Jalisco New Generation cartel in Mexico.

A criminal indictment against Molina-Lopez was announced last month. In February, Ecuadoran citizen Wilder Emilio Sanchez-Farfan was added to the sanctions listed for alleged drug shipments.

He is accused of moving tons of cocaine from processing labs neighboring Colombia to Ecuador, which are then moved north.

The US Treasury said he "is one of the most significant drug traffickers in the world today."

Known as 'Gato', he is one of the main suppliers of cocaine to the Sinaloa Cartel. He is linked to Miguel Angel Valdez Ruiz, and has started a relationship with the Jalisco New Generation cartel.

O'Toole told the Sunday World that the US delegation which announced the sanctions against the Kinahans in Dublin last month were "a pretty high-level group, for sure."

"OFAC has done this a fair amount in places like Mexico and Colombia, where we have good relationships with the government and involves something of significant national importance to that host government, even if it is not the top priority for the government."

But for such an event to happen in Europe was "not terribly normal though. It was a way showing the level of co-operation between the Irish and US governments."

"Had it not been for the Irish government I doubt this would have happened."

Daniel Kinahan's attempt to 'sportwash' his reputation through his association with boxing is unlikely to have helped his case.

"Profile certainly matters, 'El Chapo' landed himself on the sanctions list and he's a fairly colourful character in addition to all the horrible things he's done."

"Importance to a partner government can matter a lot as well. My assumption on all of this is there was a great deal of importance placed on this, probably by the gardaí, and the US used a lot of information from them in constructing this designation package."

He also said that the sanctions will probably hit the Kinahans' network a lot harder because of their use of various companies.

"I suspect these guys are going to see more day-to-day impacts than other groups. These guys seem like they were integrated into the normal international financial sector."