CELTIC has put the Green Brigade on a final warning after Uefa opened an investigation into the "setting off of fireworks" at Tuesday night's home game against Cliftonville.

The Parkhead club has an uneasy relationship with the group housed in section 111 of the stadium and now claims its behaviour is putting the club's general safety certificate at risk.

In a strongly-worded statement on the club's website, Celtic admitted the fireworks were used, causing referee Thorsten Kinhofer to ask the club's safety officers to intervene, and also revealed that 131 seats were damaged.

The statement read: "Three ­fireworks were exploded within Section 111, causing the referee to require a stadium announcement to be made instructing such behaviour to stop. As a result of this ­unprecedented step by a match official, Celtic will now be the subject of a disciplinary action for contravention of the Uefa safety and security regulations."

The statement reminded fans "the club has been under close scrutiny by the Glasgow City Council Safety Advisory Group with regard to serious safety concerns within section 111".

To that end, it also admitted that several safety concerns were evident during the Champions League second-round qualifier 2-0 win over the part-timers.

It raised concerns relating to overcrowding, the refusal of spectators to comply with stewards, mock fighting and body surfing of young people over the heads of spectators.

Only discussions between the club's supporters' liaison officer and representatives of the Green Brigade prevented section 111 being closed.

However, the club warned it will monitor the situation at both the Celtic versus Borussia Monchengladbach match tomorrow and the first leg of its third qualifier against Swedish side Elfsborg at Celtic Park next Wednesday night.

The statement continued: "It should be understood that failure to stop this unsafe behaviour will require the closure of this area in Celtic Park. The club recognises the many examples of good support for the team emanating from this part of the ground and in particular the efforts of the Green Brigade in organising positive displays which are commended.

"However, the unsafe aspects of spectator behaviour in section 111 require to be addressed with immediate effect."

Celtic has to answer a charge which allegedly breaches articles 16.2 of UEFA's disciplinary regulations.

Article 16.2 decrees that clubs are liable for inappropriate behaviour on the part of their supporters, even if they can prove the absence of any negligence in the organisation of a match, including the "lighting of fireworks or any other objects".

Celtic were fined €25,000 euros (approximately £21,000) for fans' misbehaviour in the Europa League game against Udinese in Italy in December, 2011. After the 1-1 draw at the Stadio Friuli, the Parkhead club were charged with "the displaying of a banner of an offensive nature and the setting off of fireworks by supporters".

On social media sites last night some representatives of the Green Brigade warned fellow members against setting off bangers and pyrotechnics within the section and threatened to remove them from the group.