Rotherham have condemned the "unprecedented level of violent behaviour" of a section of Millwall fans after crowd trouble marred Saturday's Sky Bet Championship fixture at the New York Stadium.
Sections of a 1,300-strong following from Millwall turned nasty after Rotherham scored an 85th-minute goal to seal a 2-1 win, which left the London club six points adrift in the bottom three.
After initially chanting for manager Ian Holloway's head, they turned their attention to the Millers fans and tried to invade home section of the ground, forcing riot police to intervene.
There were also reports of further trouble outside the ground after the game, with two stewards suffering injury and the windscreen of a car housing a disabled home supporter smashed.
The South Yorkshire club have apologised to fans caught up in the trouble and have vowed to talk with Millwall in a bid to bring the troublemakers to task.
"In planning for this fixture Rotherham United FC worked very closely with representatives of South Yorkshire Police, The Metropolitan Police and Millwall FC to try and ensure that Saturday's fixture passed peacefully," a club statement read.
"We were aware that a section of Millwall supporters were planning on attending this game intent on causing disorder.
"Contingency plans were in place to deal with this outcome with extra stewarding and Police resources in place to deal with the anticipated threat.
"Despite the extra resources deployed, this group made numerous attempts to seek disorder throughout the afternoon resulting in the despicable scenes towards the end of the match.
"Rotherham United are angered and upset at the unprecedented level of violent behaviour of some sections of the Millwall supporters inside and outside of the stadium.
"We are liaising closely with South Yorkshire Police to identify the individuals involved and our teams are already analysing all of our CCTV footage.
"We would like to acknowledge the work and bravery of South Yorkshire Police, our matchday stewards and the Stadium Safety Team who prevented a further escalation of a very serious situation.
"Further, we apologise to the innocent supporters from both clubs who were caught up in the violence, the vast majority of whom were here to enjoy a game of football.
"Rotherham United will be in contact with Millwall FC today to seek assurances that everything possible will be done to ensure the so-called fans involved in the incidents are brought to account."
Millwall responded to Rotherham's statement by issuing their own statement which read: "Millwall Football Club will do everything possible to assist Rotherham United FC and South Yorkshire Police investigating the disorder that occurred during Saturday's match at the New York Stadium.
"The club's position remains clear - anyone associated with the club found guilty of violent behaviour will be banned from Millwall matches, in addition to any punishment they receive from the authorities.
"The club will wait until all necessary investigations have been completed before we will comment further."