LONDON (AP) — Authorities in Britain, Belgium and Bulgaria arrested some 25 people early Thursday in overnight raids targeting smugglers who allegedly helped people immigrate illegally.

The U.K. Home Office said the operation involved suspects who allegedly transported migrants, most of them from Syria and Afghanistan, into Britain mainly from eastern Europe.

Investigators arrested 11 people in Britain on suspicion of assisting illegal immigration. Eight more were arrested in Belgium and seven in Bulgaria.

The migrants were often concealed in adapted vehicles. Belgian police said 110 smuggling vehicles were identified and nearly half intercepted. They said the investigation involved about 1,100 migrants.

“People smuggling is a cruel and dangerous trade in which often vulnerable individuals are treated as commodities,” Steve Dann, who directs the British agency that investigates immigration offenses tied to financial gain, said. “Many are passed into the hands of other crime gangs who would seek to exploit them for modern slavery purposes.”

Several other countries, including the Netherlands, France, Greece, Serbia and Germany, were involved in the probe that began in February.

Human trafficking gangs are solely motivated by profit, Chris Hogben of the National Crime Association said.

“We see this through migrants being sent across the channel in unseaworthy small boats or stuffed into the back of cramped lorries, vans and cars,” Hogben said. “This operation is a good example of how we can bring together law enforcement from across Europe to work together to take on that threat and disrupt the organized networks involved in people smuggling.”