MADRID (Reuters) – Spanish police have broken up a gang that trafficked hundreds of migrants across the Balkans into the European Union concealed in trucks in inhumane conditions, authorities said on Thursday.

“The investigation focused on the activities of a Spanish organization… dedicated to smuggling Pakistani nationals into the Schengen area,” said Francisco Davila Gutierrez, head of the illegal immigration unit with Spain’s national police force.

Police images showed how 77 people including four children, were crammed into a squalid cargo compartment of a small truck intercepted at the border between Bosnia and Croatia.

“These vehicles transported adults and children in life threatening situations…in overcrowded trucks at high speed on European motorways,” said Europol representative Marius Cristian Roman at a press conference.

The months-long investigation involved agencies in seven countries. The group’s leader was arrested in Romania and transferred to Spain. A further 15 people were arrested as a result of the operation, 12 of them in Spain, police said.

From their starting point at a Bosnian refugee camp, members of the gang escorted migrants on foot over the mountainous border with Croatia where they were loaded onto the trucks until reaching Slovenia or Italy. Once inside the EU, they were transferred to other countries.

Police were first alerted to the group, which charged between 3,000 and 8,000 euros ($3,466-$9,242) per trip, in 2020 when a Spanish truck driver was arrested in Slovenia with 53 Pakistani migrants hidden aboard.

Police estimate the group earned at least 2 million euros from smuggling around 400 people into the EU in recent months but said the total would be much higher as they had been operating undetected for years.

(Reporting by Nathan Allen and Guillermo Martinez, editing by Andrei Khalip, Alexandra Hudson)