Three British nationals were over the weekend arrested with over 200,000 bullets and 22 firearms in Greece.
The Iraqi-born suspects are in their 20s, a security official told the Associated Press.
There were arrested on Saturday night in two different locations.
While the two were arrested in the port city of Alexandroupolis, which is about 40 kilometres from the Turkish border, the other was apprehended near the Kipoi border point on the Evros river.
They are not believed to be on any terrorist or criminal database.
The rifles were not combat rifles, but are believed to be for training purposes.
It could not be established if the suspects had any links with ISIS.
The UK government said it had contacted Europol and Interpol.