Uefa have opened disciplinary proceedings against Celtic over the behaviour of the travelling fans in the recent victory against AIK.
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The supporters are accused of setting off flares and throwing objects.
A Uefa statement read: "Disciplinary proceedings have been opened following the UEFA Europa League play-off second-leg match between AIK and Celtic FC (1-4), played on 29 August in Sweden.
"Charges against AIK: - Stairways blocked - Art. 38 of the UEFA Safety and Security Regulations
"Charges against Celtic FC: - Setting off of fireworks - Art. 16 (2) of the UEFA Disciplinary Regulations (DR) - Throwing of objects - Art. 16 (2) DR
"The aforementioned cases will be dealt with by the UEFA Control, Ethics and Disciplinary Body on 19 September."