Cocaine disguised as charcoal with a potential street value of up to 35 million euros ($41.4 million) has been seized in a joint operation between Irish and Dutch authorities.

The drugs were found inside two shipping containers from South America that arrived at the port of Rotterdam, in the Netherlands, as part of what Irish investigators believe was an attempt to import up to half a ton of cocaine to Ireland, according to a press release from the Garda Síochána, Ireland’s national police and security service, published Wednesday.

Inside the containers were 2,000 bags of charcoal. Thanks to the use of an X-ray scanner and police sniffer dogs, some of the bags were found to contain cocaine.

Forensic Science Ireland (FSI) later confirmed that cocaine was present, but “it will take a number of days and perhaps longer for FSI to extract the cocaine from the product within which it is concealed,” reads the press release.

If the full shipment of cocaine has been discovered it could have a street value of up to 35 million euros ($41.5 million), police said.

The containers are said to have arrived at the Rotterdam port a number of weeks ago.

Arrests are expected in the near future as part of an ongoing investigation by the Garda National Drugs and Organised Crime Bureau, according to the press release.

“This is a significant development in the Garda Síochána’s effort to disrupt and dismantle organised crime groups suspected to be involved in the importation of cocaine and other drugs into Ireland,” said assistant commissioner John O’Driscoll of the Garda Síochána.

O’Driscoll emphasized the “significant international dimension” of the operation and the “importance of cooperation within the law enforcement community within Europe and further afield.”

Michael O’Sullivan, head of the Maritime Analysis and Operations Centre, which coordinates anti-drug trafficking operations by seven European Union countries including Ireland, said the seizure was “a massive seizure” that will “deal a huge blow to the organized crime group involved.”

O’Sullivan told Irish broadcaster RTÉ that Irish crime groups play a leading role in the importation of cocaine to Europe, where the market for the drug is estimated to be worth 14 billion euros ($16.6 billion).

Spain’s national police made a similar seizure of 862 kilograms (1,900 pounds) of cocaine disguised as charcoal a few weeks ago. The force said last month that a “complex chemical process” was used to give the drugs “a very similar form and color” as charcoal and “eliminating the characteristic smell of cocaine.”