Celtic have promised "the strongest possible action" as they seek to identity who threw an object on to the pitch during their win over St Mirren.

Home goalkeeper Vaclav Hladky had to be attended to after a missile landed with a loud bang near him on Wednesday.

"This kind of behaviour, indeed any form of unacceptable conduct, only serves to tarnish the reputation of the club and our own fans," Celtic stated.

"We need to all work together to make sure this stops now."

Launching a club investigation, Celtic chief executive Peter Lawwell echoed the words of manager Neil Lennon in saying the incident was "completely unacceptable".

"There have a been a number of incidents across many clubs this season, with a range of items, including pyrotechnics, being thrown on to pitches," he said. "We need to do all we can to remove this from our game.

"There are serious safety concerns associated with such behaviour and, regardless of the obvious reputational damage which this kind of behaviour has on the club, there are numerous potential repercussions which could have hugely detrimental consequences for the club and our supporters."

St Mirren manager Oran Kearney admitted he had been "tempted" to lead his players off the pitch.

Pyrotechnics are banned by law in Scottish football grounds, but smoke bombs in particular are a regular feature at games and Scottish Justice Secretary Humza Yousaf vowed to look into new legislation after Wednesday's incident.

"When I speak to the police, they tell me it is a matter of when, not if, someone is seriously injured by a pyrotechnic," he said on Twitter.

The incident followed an encroachment on to the sidelines by a small group of Celtic fans - including a man carrying a child - when Odsonne Edouard scored the opening goal against Rangers on Sunday. A steward needed treatment after being hurt in the ensuing crush.

Don't feed the 'frenzy' of 'moral panic' - Green Brigade

The Green Brigade group of Celtic supporters also appealed for information to identify the person who threw the firecracker on to the pitch in Paisley.

However, in a statement posted on social media, it accused the Scottish Government, police and judicial system of seeking to build support for "another assault on the rights of football supporters" following the repeal of the Offensive Behaviour at Football Act.

"Over the last few months, these figures have cynically sought to feed a sense of moral panic around football, casting fans as villains for their own gain," it stated.

"The mainstream media have fuelled this fire with sensationalist headlines, disproportionate coverage and click-bait journalism.

"With this in mind, it is imperative that the victory against the OBFA does not become hollow and it is clear that all fans share the responsibility to counter any attempts to replace it - which includes being responsible for your own actions and behaviour.

"While there must be a sense of perspective regarding the recent media furore, fans must realise the potential trouble they are inflicting on themselves and other fans by feeding this frenzy.

"As an ultras group, we support the safe, sensible use of pyrotechnics. However, the launching of pyrotechnics on to the park or in the direction of people is both unnecessary and counterproductive to any aspirations of normalising its use.

"Similarly, small-scale pitch invasions - whilst largely harmless - are simply giving our detractors further ammunition."