The operation "Icebreaker" broke up the gang, which is thought to have amassed an estimated 680 million euros ($760 million) in ill-gotten gains through assassinations, money laundering as well as drug and cigarette trafficking between 2016-2019, Europol said.
"Searches took place, resulting in the seizure of 8 million euros in cash, diamonds, gold bars, jewellery, luxury vehicles as well as the discovery of hidden compartments used to smuggle drugs and psychotropic substances," according to a statement cited by Efe news.
The raids took place in the early hours of May 15-16 during which the police supported by Europol and Eurojust arrested the alleged gang leader, a 48-year-old Lithuanian national, in Huelva, southwest Spain.
Police officials described the operation as the largest of its kind to date in Europe with over 450 police and customs officers deployed in Poland, Lithuania, the United Kingdom and Spain.
A substantial quantity of illicit cigarettes was also seized.
"This criminal group would traffic drugs and cigarettes into the UK, before smuggling the illegally obtained cash to Poland by different means," the police statement said.
"The money was then laundered via currency exchange offices and subsequently invested in real estate in Spain and other countries."
The suspected criminals also employed counter-intelligence technology to evade law enforcement organizations.
In what Europol described as an unprecedented collaboration between the police and Justice Departments, the Joint Operational Task Force involved the Lithuanian Criminal Police Bureau, the British HM Revenue and Customs, the Polish Police Central Bureau of Investigation, the Estonian Central Criminal Police under the Police and Border Guard Board and the Spanish Guardia Civil and Policia Nacional.
Three Europol experts were deployed to Lithuania and Poland to provide tailor-made operational support while police officers from Lithuania, Spain and Poland were aided by a system that enabled real-time exchanges of information between their national authorities.
A swift analysis of data collected during the operation also permitted the officers to adjust their strategy on the ground as required.
( With inputs from IANS )