BARCELONA, Spain -- Liverpool CEO Peter Moore has told the club's supporters to behave after six fans were arrested in Barcelona on Tuesday following disturbances in the Catalan city.

Police sources confirmed to ESPN FC that six people were detained overnight, later confirmed by Merseyside Police, ahead of Wednesday's Champions League semifinal first leg between Liverpool and Barcelona at Camp Nou.

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They were arrested after fights broke out on Plaza Reial, just off La Rambla, where hundreds of travelling supporters had gathered throughout the afternoon on Tuesday.

Images emerged on social media of the disturbances, with one video showing a fan tipping a bystander into the fountain in the middle of the square. Reports said Merseyside Police are looking to identify the man.

Police sources told ESPN FC that all of the arrests made so far were for public order offences.

CEO Moore himself took to social media to urge Liverpool supporters to treat the Catalan city with respect in the build-up to the game.

"We proudly sing that we've conquered all of Europe," he wrote on Twitter. "But let's treat this beautiful city with the respect that it deserves, and act in a manner that is befitting of LFC. By all means have a good time, but we are Liverpool, and as such, let's visit here with grace and humility."

Liverpool later added in a statement: "Liverpool Football Club is working with Merseyside Police and the authorities in Spain, who are endeavouring to identify those involved in the incident. Such behaviour is clearly totally unacceptable and will not be tolerated. It would be inappropriate to comment further while the situation is ongoing other than to confirm the club will follow due process in any and all cases of this nature."

Supporters were eventually forced out of Plaza Reial by local police later in the evening in a bid to break them up into smaller groups. But some of the travelling support told the Liverpool Echo that they felt the police's force was unnecessary.

A police source told ESPN FC they were surprised by the behaviour of a selection of the English club's following, explaining that they hadn't expected it because of the excellent way Manchester United fans conducted themselves two weeks ago.

There will be increased policing and attention throughout Wednesday -- which is a bank holiday in Spain -- to avoid further problems before the game.

Liverpool are hoping to make the Champions League final for the second successive year, while Barcelona are targeting a first final appearance since 2015.

The second leg will take place next Tuesday at Anfield, with the winners facing either Tottenham or Ajax in June's showpiece at the Wanda Metropolitano in Madrid.

Information from Barcelona correspondent Sam Marsden was used in this report.