Fans of Scottish Premiership side Celtic were caught on camera singing chants about slain soldier Lee Rigby.

Rigby was beheaded by two Daesh supporters back in 2013 so the pro-Irish fans sang in support of the IRA.

Many condemned the sick songs when the clips made the rounds online ahead of the pre-season game against Sunderland. Celtic won the friendly 5-0 but the game was marred by fighting among the fans. The fans who are believed to have been drunk sang the song, alluding to his military job.

Rigby was a corporal, drumming and handling the machine gun in the Royal Regiment of Fusiliers. The 25-year old was murdered by Michael Adebolajo and Michael Adebowale in the streets of south east London. The killers claimed they were avenging Muslims. Subsequent report shows that M15 and M16 could have done better in handling the potential danger.

The mother of the dead soldier Lyn was heartbroken about the clip.

“I haven’t stopped crying since I saw that video. Celtic need to denounce these scum wearing their team’s shirt and apologize for what they have done,” she said when interviewed.

“Everyone at Celtic is appalled by these events. Such behavior in no way represents Celtic Football Club or our supporters. We understand this incident is not subject to an ongoing police enquiry. Let us be clear, in the event that any individuals are identified as being responsible, Celtic will take the strongest possible action,” the club said.

About 21 people have been arrested from the clashes with Sunderland fans but the people caught on camera are reportedly not among them. Police should identify them soon even though fans of Celtic and Rangers have a long history of singing offensive chants as this.