Eighteen people have been arrested in Britain and France on suspicion of helping to smuggle Sri Lankan illegal immigrants into the UK, the Home Office says.
Immigration enforcement officers and Kent police carried out simultaneous raids on addresses in London, Luton and Essex at around 05:00 BST, it said.
Properties in France and Germany were also raided.
The Home Office said 11 people were held in England, and seven in France.
Those arrested in the UK have been taken to a police station in Kent for questioning. All those arrested were of Sri Lankan origin, with the exception of a 41-year-old Dutch national who was arrested in Kent.
Officers also seized computers, documents, cash and mobile phones from a number of addresses.
The pan-European operation follows a joint investigation involving Home Office immigration enforcement investigators, Kent Police, the Serious Organised Crime Agency (Soca), Europol and French and German law enforcement agencies.
Those under arrest are suspected of being part of an alleged criminal network that smuggles Sri Lankans into the UK in vehicles through Channel ports at a cost of about £4,500 per person.
Rob Allen, assistant director for Immigration Enforcement Criminal and Financial Investigations, said: "People smuggling is an international crime which requires international co-operation, and the arrests made today show that co-operation is yielding results.
"We believe this operation will have a significant impact on an organised network we suspect has been a major player in terms of bringing Sri Lankan nationals to the UK illegally."
He added: "Our investigation will continue with the evidence we have seized today."
Deputy Chief Constable of Kent Police, Alan Pughsley, said: "This sends a strong message to the criminals who seek to use our ports in this illegal trade - we will work together with UK and overseas partners to track you down and bring you to justice."
Details of arrests in the UK are as follows:
- 38-year-old man arrested at address in Balmoral Drive, Hayes
- 50-year-old man arrested at address in Aurelia Road, Croydon
- 51-year-old man arrested at address in Rayners Lane, Harrow
- 46-year-old man arrested at address in Brick Lane, Northolt
- 33-year-old man arrested at address in Bradley Road, Luton
- 33-year-old woman arrested at address in Mitcham Road, East Ham
- 32-year-old man arrested at address in Drenon Square, Hayes
- 24-year-old woman arrested at address in Salisbury Avenue, Southend
- 31-year-old man arrested at address in Salisbury Avenue, Southend
- 29-year-old woman arrested at address in Salisbury Avenue, Southend
- 41-year-old man arrested after attending a police station in Kent