Spain's Civil Guard and National Police forces arrested 26 suspected members of the Italian Camorra mob accused of laundering mafia money through companies in Spain, prosecutors said.
Officers arrested the suspects in raids in Madrid and seized cash, firearms and drug-related material, the anti-corruption prosecutor's office said in a statement.
"Those detained belonged to various clans in the Camorra and operated in Spain in connection with criminal organisations in Italy," it said.
"They created a business network in Spain in order to introduce earnings from their criminal activity into Spanish financial channels."
The suspects are due to go before a judge for questioning, accused of drug-trafficking, membership of a criminal gang, money-laundering, forgery and tax fraud, the statement said.
Tuesday's raids began at around 7am with around 30 people targeted in the sting operation.
The operation — known as Operation Tarantela — was headed up by Spain's High Court and the country's anti-corruption prosecutor.
The Camorra mafia clan is originally from Italy's Campania region and its capital Naples.