One of the largest criminal networks smuggling drugs and people in the western Mediterranean has been dismantled, authorities have said.

Europol said 78 people were arrested in Spain and Algeria in a bust of the network, that is also linked to other criminal activities including “violent robberies, extortion, illegal detentions, and money laundering”.

The group moved synthetic drugs from Spain and Portugal to Algeria, then used the return journey to smuggle migrants and weapons to the Spanish mainland and island of Ibiza on “ghost speedboats”.

Some of the items seized included 18 high-speed vessels valued at €5m (£4.2m), guns, more than €25,000 (£21,400) in cash and 15,000 MDMA pills.

The sting, led by Spanish police, involved searches in 17 locations in Spain, including Alicante, Almería, Cartagena and Murcia.

Europol said the group had “evolved from drug trafficking into a duel-flow criminal enterprise designed to maximise profits” with outbound routes from Spain and Portugal to Algeria.

“The smuggling focused on synthetic drugs (such as MDMA), firearms, and explosives. Along routine routes from Algeria to Spain, the group smuggled migrants, charging up to €12,000 (£10,200) per person,” Europol’s statement said.

“In just one trip, over 50 migrants could be smuggled. All in all, profits from migrant smuggling alone are estimated to be more than €24m (£20m).”

The network also provided services to other organised crime groups, “facilitating the movement of illicit goods and people across the Western Mediterranean”.

“Investigators believe the network coordinated multiple trafficking flows. Synthetic drugs, and sometimes people, were moved from France and Spain to Algeria, while cannabis resin, weapons, and migrants were transported from Algeria to Spain.”

Often, the group used a fleet of high-powered speedboats to conduct rapid maritime operations. This included “ghost speedboats” which are designed to avoid registration and detection, which are prohibited in Spain.

“The group used these boats to organise transfers in international waters near the Spanish coastline,” Europol said. “Once the cargo or migrants were handed over at sea, other network members arranged onward transport by land.

“Migrants were often carried in overcrowded boats without lighting or life jackets, frequently under extreme weather conditions.

“Investigators believe suspects perpetrated sexual assaults, physical abuse, and placed migrants in inhuman conditions in makeshift housing.”

The suspects were primarily of Algerian origin and had connections to criminal groups in France, Belgium, Portugal, Italy and Poland.

Other objects seized in the police sting included satellite phones, GPS devices, encrypted communication tools and satellite dishes.

The announcement comes a week after roughly 78,000 migrants fled into the Spanish North African territory of Ceuta that was blamed on online rumours about an open border.

Most of the migrants returned to Morocco but between 3,000 and 5,000 remain in the territory, the exclave’s leader Juan Jesús Vivas said.