Uefa have opened disciplinary proceedings against Arsenal, Galatasaray, Basle and Borussia Dortmund following crowd disturbances during Wednesday night's Champions League ties.
Several flares were thrown onto the pitch from the section where the 3,000-strong travelling Galatasaray supporters were located towards the end of the first half at the Emirates Stadium, causing the Group D match against Arsenal to be briefly halted.
Metropolitan Police confirmed there had been six arrests as part of their operation for the European tie in north London, two of which were for entering the ground with flares.
Uefa view it as the home side's responsibility to search supporters for any illegal items before they come into the stadium.
At St Jakob Park, a battery appeared to be thrown in the direction of the assistant referee near to the Basle goal during the tie with Liverpool, while at Anderlecht's stadium, flares were lit in the area housing travelling Borussia Dortmund fans.
If found guilty, the clubs could be hit by a fine from the European governing body, or be ordered to play matches behind close doors.
A Uefa statement included a reference to Arsenal's charge for what is understood to be a minor possible sanction and also confirmed that the cases involving all clubs will be dealt by the Control, Ethics and Disciplinary Body on Thursday October 16.
Arsenal expressed disappointment over the events on Wednesday evening.
There were disturbances before the match, when Galatasaray fans had let off flares in streets around Finsbury Park and thrown some into the Tollington Arms pub.
A strong Police presence was on the ground outside the stadium, while Arsenal stewards conducted searches of bags on the turnstiles, when at least half-a-dozen flares and fireworks were confiscated.
Despite that action some were still able to be smuggled in by Turkish supporters.
Arsenal also reported damage to around 100 seats in the away end and they will now co-operate fully with Uefa when asked for their observations.
An Arsenal spokesman said in a statement: "Crowd safety is always a top priority for us and we were disappointed with the incidents last night, which occurred despite extensive searches of away supporters as they entered the stadium and close liaison with police, Uefa and visiting club officials."