Disturbances involving a small number of Northern Ireland fans in France were short, minor, and were not started by them, police said.
French troublemakers created the problem in the south coast city of Nice on Saturday night but there was no fighting with supporters of Sunday’s opponents Poland, the PSNI said.
Supt Nigel Goddard said: “It is disappointing that a small number of Northern Ireland fans responded but it was only a short and minor incident.”
It is understood a small number of supporters were injured during the face-off near the Place Massena.
French riot police were called in to disperse local “ultras” who attacked the Northern Ireland football fans, a senior supporters’ representative said.
Gary McAllister, chairman of the Northern Ireland supporters’ clubs, tweeted: “Local ultras attacked Polish and NI fans who were mixing well.
“French riot police dispersed locals.”
Thousands of Northern Ireland and Poland fans have converged on the city on the Mediterranean coast for Sunday’s fixture.
There were noisy but peaceful scenes throughout Saturday and many examples of friendly banter between the two sets of supporters.
Revellers partied into the small hours in the area around the Place Massena under the watchful eyes of French police.