A Glaswegian is among four men arrested on suspicion of attempting to traffic children into the UK.
The arrests follow a National Crime Agency (NCA) investigation into a group suspected of transporting migrants from Europe in the back of lorries.
Officers found ten 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.”
West Flanders prosecutor Frank Demeester added: “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.”