Riot police with batons were deployed against Aberdeen fans as fighting broke out after the side's Europa League match in Cyprus.
The match itself was interrupted when supporters of Apollon Limassol threw flares onto the pitch.
More trouble erupted after the Dons 2-0 defeat, as a small number of fans at the Aberdeen end clashed with stewards at the AEK Arena in Larnaca.
Police with batons and riot shields then moved in.
BBC Scotland's Scott Davie described "ugly scenes" between fans and stewards.
Aberdeen manager Derek McInnes later criticised stewarding at the match and said fans had been treated badly.
He told BBC Radio Scotland: "We expected it to be a bit volatile. We expected there to be plenty of passions from the side but it did boil over at times.
"I'm hearing our fans were treated terribly by the stewards here as well. Steaming in with flares and tear gas and everything else to try to defuse the situation.
" I didn't get to see it but I'm hearing it second hand. And when you see some of the stuff that was going on.
"Things getting thrown onto the pitch, people spitting into the dugout, players getting thrown on.
"That's when you should have seen the stewards being more visible, not treating our fans the way they did."
The flare incidents took place early in the second half, with one landing inside the goal behind Dons goalkeeper Joe Lewis.
Television footage caught Swiss referee Stephan Klossner tell an official that he would abandon the match if behaviour did not cease but it calmed down.
In a statement Aberdeen FC said it had "commenced dialogue with the stadium operators, Apollon Limassol and the authorities" about the events.
It added: "As part of this, the club has requested that CCTV footage is interrogated in order to assist matters.
"The club will not be making any further comment until the conclusion of this comprehensive investigation."
Source: BBC NEWS