A man from Northern Ireland was among four people arrested as part of a National Crime Agency (NCA) investigation into a crime gang suspected of smuggling migrants into the UK.
The arrests come after the discovery of 10 migrants 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.
Belgian police were acting on information from the NCA, and arrested the driver of the lorry, a 64-year-old man from Glasgow.
NCA officers then arrested three further men.
Two Irish nationals aged 39 and 48 were detained in Dover on suspicion of facilitating illegal immigration.
A 30-year-old man was subsequently arrested in Co Antrim on Friday.
All three men remain in custody being questioned.
Officers have carried out searches at properties across Northern Ireland and Kent. At an address in Kent two suspected firearms were seized.
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.
“We have seen only recently in Essex the tragic consequences which these types of attempts can have.
“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 cooperation 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.”