Arsenal boss Arsene Wenger expects UEFA investigation into crowd trouble as 20,000 Cologne fans cause chaos at Emirates Stadium

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Arsene Wenger expects UEFA to launch an investigation into the crowd disturbances which threatened Arsenal's Europa League clash against Cologne.

The Gunners ran out 3-1 winners in the Group H opener, which was delayed by an hour after away supporters caused havoc outside the stadium.

As many as 20,000 Cologne fans are believed to have made the journey from western Germany despite only 3,000 tickets being made available.

There was crowd chaos at the Europa League match between Arsenal and Cologne as 20,000 fans of the German club, many without tickets, descended on the Emirates Stadium 

Police had to move quickly to keep the Cologne fans outside the ground under control

Cologne supporters were stopped on a walkway as they tried to get to the Emirates 

Arsenal manager Arsene Wenger anticipates a UEFA investigation into the crowd trouble

That meant many attempted to enter without tickets or with tickets for the Arsenal sections, where it soon became clear ahead of kick-off that plenty had succeeded.

Five arrests were made as the Metropolitan Police said that additional officers had been deployed to the area following the unrest.

Substitute Sead Kolasinac volleyed Arsenal level after they went in at half-time trailing to Jhon Cordoba's long-range effort.

Alexis Sanchez and Hector Bellerin struck to seal the three points from the match but it was off-pitch actions which Wenger believes may now be scrutinised.

Cologne fans clashed with stewards, brought in flares and sat in home sections but it is likely to be Arsenal - as organisers of the match - who face potential sanctions.

Riot police moved in with dogs as a precautionary measure on Thursday evening

Some Cologne fans with tickets for Arsenal sections tried to hurdle barriers into the away end 

Asked if UEFA should take action, Wenger replied: 'They are the only master to analyse the facts of what happened. They will certainly make an inquiry to see what happened, for sure.

'They (Cologne fans) were very clever.

'I don't know how they managed to infiltrate our fans and get everywhere but they did that very well. I don't know if they went through Arsenal membership, on the internet... they did very well.

'We waited patiently in our dressing room but what was difficult was for me was I had all kind of plans to think about at some stage

Riot police moved into the section where the away fans had been housed after fights broke out

Thursday night's match was delayed for an hour as the situation was brought under control 

'It was all kind of speculations you know that we had to analyse and see how we can deal with the situation. But in the end at some stage I thought they would not play the game, because I can't see the police taking any risk.

'We live in a society of 100 per cent security and I thought they would never take a gamble to play this game when I saw the images around the stadium. But I must say our supporters as well dealt well with the situation as well and there was no aggravation.'

Cologne coach Peter Stoger refused to be questioned on the actions of the club's supporters: 'I have no comment about the fans,' he said.

'I'm the coach, my job is the team, my job is football not the fans.'

A club spokeswoman added: 'We have to first inform ourselves and in the next few days we will talk about that.'