Authorities say they broke up one of the largest criminal networks running migrant smuggling in the Western Mediterranean.

Spanish authorities, working with Europol and police in France, Portugal and Poland, have dismantled what they say is one of the largest criminal networks for migrant smuggling, illegal drugs and weapons trafficking across the Western Mediterranean.

Launched by Spain’s Civil Guard and National Police in 2023, the operation culminated in an “action day” on June 16, Europol said on Friday, leading to 78 arrests and the seizure of assets, including 18 high-speed boats.

Officials described the crossings as extremely dangerous, with migrants crammed into overcrowded boats travelling at high speed through rough seas, often without lighting or life jackets.

Authorities said passengers were sometimes tied down to keep them from falling overboard, and that the organisation used extraordinary violence against migrants, its own members and police.

The operation “successfully dismantled one of the ⁠most complex, active and dangerous transnational criminal networks detected to date in the Mediterranean,” Spain’s Civil Guard said in a statement.

Of those detained, 77 were arrested in Spain and one in Algeria, including three high-value targets. Most were Algerian nationals with ties to criminal groups in France, Belgium, Portugal, Italy and Poland.

As part of the operation, 17 locations were searched in Spain, including in Alicante, Almeria, Cartagena and Murcia.

The announcement on Friday comes a week after a mass migrant surge into Spain’s North African enclave of Ceuta drew international attention to migration pressures in the region.

The criminal network, described as operating like a logistics company for organised crime groups, managed two-way maritime smuggling routes between Europe and Algeria, according to Europol.

The network allegedly moved synthetic drugs southward and migrants northward to Spain’s southeastern coast and the island of Ibiza.

Investigators say the network carried out at least 64 migrant-smuggling operations, bringing more than 2,000 people into Spain and generating over €24 million ($27m) in profits, charging as much as €12,000 ($13,800) per migrant and packing up to 50 people onto a single boat.

Authorities also found that the network provided a wide range of services to other criminal organisations, including vessel storage, transportation, refuelling, maritime transfers, boat maintenance and counter-surveillance.

The network reportedly moved money through informal hawala networks, making it difficult for investigators to trace illicit funds.