Fourteen people were arrested at Belfast’s two airports and the docks over a three-day period by the Home Office’s Immigration Enforcement.
It was part of a UK-wide operation targeting organised crime groups using the Common Travel Area (CTA).
The CTA is a special travel zone covering the United Kingdom, Republic of Ireland, Isle of Man and the Channel Islands.
Under its rules, UK and Irish citizens can travel freely between the countries.
However, CTA rights do not extend to migrants, even if they hold lawful residency in the UK or Ireland.
Over three days, the Home Office said 14 immigration offenders – including seven Albanians – were detected at Belfast International Airport, Belfast City Airport and Belfast Docks as they attempted to travel to Great Britain.
All had entered the UK illegally by abusing the CTA, the Home Office added.
One man from Iran was detained at Belfast City Airport after he was found with three false documents displaying his image.
He had flown into Dublin Airport the previous day.
Johnny Evans, an inspector with the Home Office’s Immigration Enforcement, said the operation aimed to “disrupt and dismantle” organised gangs which are exploiting the CTA as well as vulnerable adults and children.
“Quite often people are coming from war-torn countries and we accept that there are safe and legal routes into the United Kingdom,” he told BBC News NI.
“People are often exploited, they’re held for large sums of money and often are put into things like debt bondage to try and work off these debts.”
Officers checked foot passengers arriving by ferries, as well as profiling vehicles of interests.
Mr Evans said: “We’ve also arrested people that pose a significant risk and harm to the United Kingdom, people who have previously been deported for very serious offences.”
During the operation across Northern Ireland, Scotland, Holyhead in Wales and London’s Luton Airport, a total of 31 immigration offenders were arrested for abusing the CTA.
Ten false identity documents were seized, as well as £400,000 in criminal cash seized.
In Northern Ireland, a Somali national was arrested at asylum accommodation in Belfast on behalf of Danish authorities on suspicion of a “gangland murder” in Denmark in 2022.
A joint police and Immigration Enforcement operation safeguarding visit was also conducted at a mushroom factory in County Armagh over the safety of foreign national workers.
A number of interventions also took place on Northern Ireland’s road networks including the seizure of £400,000 found in a vehicle on the A1 which was linked to serious organised crime.