A number of Irish men are among four people arrested on suspicion of attempting to traffic children into the UK.
The arrests follow a UK National Crime Agency (NCA) investigation into a group suspected of transporting migrants from Europe in the back of lorries.
Officers found 10 people being trafficked in a lorry carrying a load of tyres near Ghent in Belgium on Thursday.
The migrants, believed to be two adults and eight juveniles, are thought to be from south-east Asia.
Acting on information from the NCA, Belgian authorities arrested the driver of the vehicle, a 64-year-old man from Glasgow. NCA officers also arrested two Irish men, aged 39 and 48, in Dover on suspicion of facilitating illegal immigration. A 30-year-old man was subsequently arrested in Co Antrim, Northern Ireland, on Friday.
The latter three are now in custody being questioned by NCA investigators.
Searches have been carried out at properties in Northern Ireland and England, with officers seizing two suspected firearms at an address in Kent.
NCA regional head of investigation Gerry McLean said: “Our close working with our Belgian partners in this instance has led to the safeguarding of a number of migrants who had been put in a very dangerous situation, and we are grateful for their support.
“Working with partners at home and abroad, we are determined to do all we can to disrupt and dismantle criminal networks involved in illegal immigration, and our investigation into this matter continues.”
West Flanders prosecutor Frank Demeester added: “This kind of human smuggling is very dangerous and the operation proves once more that international co-operation works in the fight against this type of organised crime.
"The contacts between the British NCA and Belgian Federal Judicial Police, maritime police and prosecutors have become more intense in recent years.
“In the fight against human smuggling, the UK is obviously an important partner as being the country of destination.” –PA