Liverpool are to "establish the facts" following reports of "heavy-handed" treatment at the hands of police and stewards in Tuesday's Champions League clash at Sevilla.
Supporters group Spirit of Shankly claimed that some travelling fans were refused entry into the Ramon Sanchez Pizjuan Stadium, while others were assaulted by police.
A statement released by the group's chairman Jay McKenna to ESPN read: "We became aware of issues affecting supporters during the first half of the match.
"A couple of our committee members reported problems getting into the ground, being refused access as the flag they had [which featured a Liver bird and the word "defiance"] was accused of having a political message.
"What is more concerning is the reports of heavy-handed treatment of supporters, including physical assaults, with one committee member reporting she was punched as she was pushed out of the ground.
"Similar experiences have been shared with us from other supporters last night, and we've asked people to come forward so we can raise this issue with the club.
"We've already flagged it up to them and we're aware they are looking for more information.
"Clearly, though, what happened last night isn't acceptable and we will be asking both clubs and UEFA what they plan to do about it."
UEFA is reportedly aware of the problems fans had in accessing the stadium, and Liverpool are looking into the alleged incidents.
"Following detailed and troubling accounts given by Liverpool supporters attending the match against Sevilla last night, the club is seeking to establish the facts regarding their treatment at the hands of the host stewards and local police force," a club statement read.
"The safety and security of our supporters is our paramount concern and we intend to gather all the relevant information before responding further."
Liverpool drew the game 3-3 having seen a three-goal half-time lead wiped out by Sevilla.