Police have arrested 13 people over “serious public disorder” at a rally held by Tommy Robinson before the European Parliament elections.
Violence broke out after a large group of men calling themselves the Muslim Defence League (MDL) converged on the event in Oldham on 18 May.
Supporters said they wanted to protest against Robinson’s election campaign, but footage posted on social media showed numerous members of the group with their heads and faces covered.
“Look at the soldiers behind us,” said one member of the group. “We’re Halifax Pakistanis reppin’ in Oldham, and reppin’ for the MDL.”
Police initially escorted the demonstration, but violence broke out after they arrived at the pro-Robinson rally at a park in Limeside.
Officers were pelted with bricks and eggs as they attempted to keep the two groups separate, seeing vehicles damaged.
Greater Manchester Police launched an operation codenamed Woodville into the “serious public disorder”.
In a series of dawn raids on Wednesday, they arrested 13 men and boys in Oldham and Crumpsall.
The suspects, aged between 15 and 40, were arrested on suspicion of violent disorder.
Investigators have also released the images of 26 people that they want to speak to.
Ch Supt Neil Evans said police were “treating May’s disturbance with the upmost seriousness”.
“We have been in liaison with the Crown Prosecution Service since the early stages of the investigation and a team of detectives has been working to identify those whose criminal behaviour resulted in the ugly scenes witnessed,” he added.
“We understand and respect the right to peaceful protest and counter-protest. However we will not tolerate it when this crosses into criminal behaviour.
“Accordingly, we can and will respond when that line is crossed."
Ch Supt Evans said several people involved had travelled to Oldham from outside Manchester, and that police were liaising with neighbouring forces.
“We must continue to work together as a community and support the justice process so that criminal behaviour is appropriately and proportionately challenged,” he added.
It was one of several disturbances during Robinson’s election campaign, which saw the English Defence League founder “milkshaked” and fights break out between supporters and opponents.
Robinson, who ran as an independent MEP for North West England, finished in eighth place with 2.2 per cent of votes.
Two months later, he was jailed for contempt of court for a second time over a video discussing grooming gang trials that were subject to reporting restrictions.
Robinson, whose real name is Stephen Yaxley-Lennon, was released from prison in September.
Police continue to pursue several of his supporters over "Free Tommy" protests where officers were attacked in London.
Anyone with information on the Oldham incident is asked to contact police on 0161 856 6551, or call Crimestoppers anonymously on 0800 555 111.