Two people were arrested at the UK border last weekend after 15 Iranian nationals tried to enter England by sea.
In one incident, eight people were found on a vessel off the Kent coast, after patrol boats were deployed to it.
They were taken to Dover and two of the group arrested on suspicion facilitation, though they have since been released under investigation.
Separately, seven people were intercepted at Dover Western Docks by Border Force and Kent Police.
It is believed they arrived using an inflatable boat, which has been located and seized.
All 15 said they were Iranian nationals and enquiries are ongoing to determine if both incidents are linked.
A spokesperson for the Home Office said: “The 15, who all presented themselves as Iranian, were interviewed and must now report regularly to the Home Office while their cases are progressed in line with the UK immigration rules.
“Two individuals arrested on suspicion of facilitation have been released under investigation.
"Immigration Enforcement’s criminal investigation remains ongoing and it would therefore be inappropriate to comment further.”
