Tear gas was used by French police when supporters were detained in crowded areas around the Stade de France, causing safety fears to spread among those present.
“This is the biggest game in European football and the fans shouldn’t have to live through the scenes we witnessed tonight.
“We have officially requested a formal investigation into the causes of these unacceptable issues.”
European football’s governing body UEFA said the problem was caused by people without valid tickets trying to enter the stadium and that tear gas was used to maintain control.
“This led to a conglomeration of fans trying to get in. As a result, kick-off was delayed by 35 minutes to allow access for as many fans as possible with real tickets.
“As the numbers outside the stadium continued to build up after kick-off, the police dispersed them with tear gas and forced them out of the stadium.
“UEFA expresses its sympathy for those affected by these events and will urgently investigate this matter further together with the French police and authorities, as well as the French Football Federation.”
Photos showed fans crammed into fenced off areas after a bottleneck formed around a particularly tight entry point at the Liverpool end.
Many fans with tickets say they were prevented from entering the stadium in dangerously crowded areas and poor communication with security.
“People without tickets broke through the barriers and tried to get into the stadium to watch the game,” a spokesman for the Paris Police Prefecture told CNN. “These attempts triggered mass movements.”
As confusion spread ahead of kick-off, videos surfaced on social media of people – with no clear team affiliation – scaling fences around the stadium and running into the ground.
The game eventually started but there were many empty seats at the Liverpool end of the stadium.
Merseyside Police, who attended the match as observers and advisors, said: “The vast majority of supporters behaved in an exemplary manner, arriving at the turnstiles early and queuing as instructed.”
“We know people would have witnessed many harrowing scenes last night and we wish everyone returning home from Paris a safe journey.
“Our focus today will be to assist Liverpool City Council in overseeing the homecoming parade.”
After the game, Liverpool manager Jurgen Klopp said the team was aware of what happened before the game and that their families were affected.
“I haven’t been able to speak to my family yet, but I know the families have had a lot of trouble getting to the stadium,” he said.
“I heard a few things that weren’t good, it was obviously quite difficult out there, but I don’t know more about that.”