Three Irish men arrested over vandalism in a bar in Poznan have been released ahead of Republic of Ireland's Euro 2012 opener against Croatia on Sunday night.
The trio were detained around the same time as 10 Polish and one Croat man were taken into custody after violence broke out in the Stary Rynek part of town.
It is understood the Irish men were with a large group of people from other countries when bottles, glasses and a lamp were smashed in a bar in the old market square.
It was described as pre-match celebrations getting out of hand.
Dozens of riot police were dispatched to the square to restore order at around 3am on Sunday after fighting broke out among a small number of fans.
There was further minor clashes between some Polish and Croat fans and riot police were deployed a second time.
The Mayor of Poznan Ryszard Grobelny attempted to play down the incident.
"This is an isolated incident. This kind of incident is not unusual with a gathering of this size and the fans' behaviour has normally been excellent," he said.
Mr Grobelny insisted that the police action stopped the violence spreading.
"I would not want to see any incidents of this kind happening. But when you have thousands of fans and many litres of beer drunk these incidents are sadly inevitable," he added.
The three Irish men were detained on suspicion of public order offences, vandalism and damage to property.