Liverpool have issued a statement apologising to Manchester City after the visitors' team bus was damaged by missiles thrown as it arrived at Anfield for the Champions League match.
Liverpool fans threw bottles and fireworks at the Manchester City coach as it arrived at Anfield.
A number of red flares were also let off, making visibility difficult as supporters lined the streets outside the stadium.
The atmosphere had been vibrant with a number of people climbing up lampposts, walls and road signs to catch a glimpse of the teams as they arrived.
City arrived first but their bus became a target for a few missiles as it slowed to navigate the corner of Arkles Lane and Anfield Road, where most of the fans were gathered.
Liverpool arrived to a raucous welcome moments later.
A Liverpool statement read: "The club condemns in the strongest possible terms the scenes which preceded our Champions League quarter-final, which resulted in damage being inflicted on the Manchester City team bus during their arrival at Anfield.
"We apologise unreservedly to Pep Guardiola, his players, staff and officials caught up in the incident.
"The behaviour of a number of individuals was completely unacceptable and the club will co-operate fully with the authorities to identify those responsible.
"The priority now is to establish the facts and offer Manchester City whatever support is necessary."