Trouble has broken out during Dundee United's 2-2 draw with Dinamo Moscow at Tannadice Park.
About 150 fans of the Russian club had travelled to Dundee for the Europa League qualifying third round match.
Violence flared in a stand in the first few minutes of the game, before police and stewards managed to separate the two sets of supporters.
Several men - who appeared to be Dinamo Moscow fans - were seen climbing up into the top tier of the stand.
BBC Radio Scotland's match commentator Jim Spence told listeners that fans of both clubs appeared to have been throwing punches.
He told listeners: "There's a real scrap going on in there. There's a steward trying his best to get in among it and there's about five or six policemen in there trying to stop it.
"I can see United fans in there and I have to say they are throwing plenty of punches and the Russians are throwing plenty of punches."
Co-commentator Allan Preston added: "It seems to be the corporate end - it's all shirts and ties. There are about 30 or 40 people involved, standing trading punches".
The match was able to continue while police and stewards restored order.
Speaking at half time, BBC Sportsound presenter Richard Gordon said: "I have to say I cannot remember the last time I saw fighting like that inside a Scottish football ground.
"We are up in the commentary gantry which is above the fans in the main stand. The Russian fans are in what used to be the old enclosure, down below at pitch level.
"There were clearly some Russian fans who were also up in the main part of the stand. I've no idea what happened but it all kicked off. There were certainly Russian fans in there but there were most certainly United fans. There was punching, there was kicking.
"There was one guy - someone had gone down and he was obviously absolutely determined to give him a right good kicking. He was pushing stewards out of the way.
"I saw some Russian fans climbing up onto the barriers and the walkways, trying to get up towards the fans there. I hate to say it, but United might well be in bother".