FAN behaviour at Sunday's Old Firm clash was the "worst in 15 to 20 years", a police leader has said.

David Hamilton, vice-chairman of the Scottish Police Federation, said match authorities are battling "an escalation in violence".

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It comes as the 47-year-old fighting for his life after a mass street brawl in Glasgow between rival fans was named as Francis McCann, from Drumpchapel.

The Celtic fan, who was stabbed in the neck during the fight in the Merchant City area, remains critically ill in hospital.

Police are treating the attack as attempted murder and investigations are ongoing.

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Two other men, aged 29 and 30, were also stabbed in what Police Scotland have described as serious assaults.

The incident, which broke out shortly after 5pm on Sunday March 31, came just hours after a bad-tempered 2-1 showdown between Celtic and Rangers at Parkhead stadium.

Mr Hamilton said the behaviour of players had been unacceptable during the match, exacerbating tensions between fans.

Rangers pair Alfredo Morelos and Andy Halliday were shown red cards for clashes with Celtic captain Scott Brown.

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Brown had celebrated in front of Rangers fans at full-time led to a bust-up with Halliday which sparked a mass fracas.

Some Celtic fans spilled on to the pitch after their side's opener and flares were also thrown during the match.

Mr Hamilton told BBC's Sportsound: "It's despairing the way some fans are behaving in Scottish football," Hamilton said. "We're seeing an escalation in violence both in terms of severity and frequency.

"At the weekend, some of the officers who were working at Celtic Park were saying it's the worst they've seen in 15-20 years of service.

"An officer had a flash-bang thrown at him that just missed his head."

It comes amid warnings from Justice Minister Humza Yousaf that he will not rule out legislating for strict liability, which would see clubs held responsible for fans behaviour at grounds.

Campaigners believe it would help tackle sectarianism and hooliganism.