Spanish police say they have smashed a highly sophisticated trafficking ring that smuggled about 1,000 people from Syria and Algeria into Europe by boat.
Migrants from Syria were illegally transported via Lebanon and North Africa to the coast of Algeria for about €20,000 ($21,700) per person, it is alleged.
From Algeria, they were sent across the Mediterranean in overcrowded boats and taken to unsanitary safe houses in Spain, police said.
Police said the smugglers used hidden microphones, spy cameras and several frontmen and branch networks in Spain to run their operations.
In another sign of their "specialisation and professionalisation", they allegedly drew up detailed smuggling routes to evade police and sold their knowledge to other criminal gangs.
A total of 21 people were arrested in police raids in which four hotels were searched, three vehicles impounded and thousands of euros, US dollars and Algerian dinars seized.
Six alleged ringleaders are in custody after the raids, which took place in June but have only now been revealed by Europol and Spanish authorities.
The sea crossings were "extremely dangerous" and "migrants' lives were put at risk" in boats without safety equipment, food or water, Europol said.
About 750 migrants from Syria, and 250 from Algeria, are believed to have travelled to Spain on the boats loaded with fuel canisters.
The Syrians were smuggled over a land border into Lebanon and flown from Beirut into Egypt, it is alleged, before heading west across North Africa.
Detectives say the smuggling route continued via Libya and Tunisia, before migrants reached the criminal gang's base in Algeria.
Police say they were placed in temporary accommodation on the Algerian coast before setting off from the coast of Oran or Mostaganem.
It is claimed they had to pay at each stage using the informal hawala payment system, with the hidden cameras and microphones used to "guarantee the collection of money".
Two branches of the trafficking ring are said to have operated in Spain, with one working on the coast of Almeria and Murcia to pick up landed boats.
Europol said the migrants were transported to Madrid, where a second branch ran operations, and placed in overcrowded housing.
When the houses became too full, the traffickers turned to local hotels that they "controlled" and hid dozens of people there, police believe.
Investigators say the network arranged passports and plane tickets for the migrants to continue their journey beyond Spain. Several hotels were searched as part of the raids, while 25 bank accounts were frozen.
More than 28,000 people have arrived in Spain by sea this year, according to the UN's refugee agency UNHCR, more than in some entire years.
The majority arrive via the Canary Islands off Africa's west coast. About 4,000 have arrived on the mainland and 1,600 in the Spanish enclaves of Ceuta and Melilla, which border Morocco.
