Large-scale disorder broke out in Leicester on Saturday, with police and community leaders calling for calm.
Officers tried to hold back crowds amid tensions involving mainly young men from sections of the Muslim and Hindu communities.
Police said two arrests had been made, and that the trouble flared up after “an unplanned protest”.
It is the latest of several incidents, including violence after an India and Pakistan cricket match on 28 August.
A significant police operation will remain in the area in the coming days.
Suleman Nagdi, of the Leicester-based Federation of Muslim Organisations told the BBC: “What we have seen on the streets is very alarming.
“There have been problems in the community since the India and Pakistan cricket match and while that game often sparks gatherings they have not in the past turned this ugly.
“We need calm – the disorder has to stop and it has to stop now. There are some very dissatisfied young men who have been causing havoc.
“We need to get the message out that this must end and try to do this through parents and grandparents talking to their sons.”
Sanjiv Patel, who represents Hindu and Jain temples across Leicester, said he was deeply saddened and shocked by Saturday night’s disorder.
He said: “We have lived in harmony in the city for many decades but over the past few weeks it is clear there are things that need to be discussed around the table to get out what people are unhappy about.
“Resorting to violence is not the way to deal with this.
“We are horrified and deplore what was going on (yesterday) and across the last two weeks.
“Across the Hindu and Jain community and with our Muslim brothers and sisters and leaders we are consistently saying ‘calm minds, calm heads’.”
He warned people to be wary of disinformation on social media.
He added: “Violence is not a solution to anything. This has to be a time for peace, calm and engagement.”
Police said one man was detained on suspicion of conspiracy to commit violent disorder and another on suspicion of possession of a bladed article.
They remain in police custody.
Leicester city mayor Sir Peter Soulsby said: “I don’t think anyone saw the confrontation (on Saturday) as a likely outcome and police had been given reassurance things were calming down a lot.
“Things got very nasty indeed last night and I am very worried on behalf of the people who were caught up in it and I was impressed by the way police responded to it – it can’t have been an easy task.”
He added: “It’s mostly young men in their late teens and early 20s and I have heard suggestions people have come in (to the city) from outside looking for an opportunity to have a set to.
“It’s very worrying for people in the areas where this has happened.”
Sir Peter said it was important community leaders continued to try to de-escalate the situation but he acknowledged it was a challenge to get through to young people.
Speaking on Saturday night, Leicestershire Police’s temporary chief constable Rob Nixon said in a video: “We’ve had numerous reports of an outbreak of disorder in parts of the East Leicester area of the city.
“We have got officers there, we are taking control of that situation, there are additional officers that are en route, and dispersal powers and stop and search powers have been authorised.
“Please do not get involved, we are calling for calm.”
Community leaders from East Leicester were on the ground with officers, and were calling for calm and encouraging people to go home, the force added.
In the early hours on Sunday, police said the situation was calming and “under control”, and large number of searches had been carried out.
“Several incidents of violence and damage have been reported to the police and are being investigated,” a spokesperson said.
“We are aware of a video circulating showing a man pulling down a flag outside a religious building on Melton Road, Leicester.
“This appears to have taken place while police officers were dealing with public disorder in the area. The incident will be investigated.”
‘Out of control’
A woman who witnessed Saturday’s disturbances said there were people wearing balaclavas or with masks over their faces, and with hoods pulled up.
She told the BBC they were “just everywhere, it was like crowds walking away from a football match”.
“There were police blocking the road; officers literally stood shoulder to shoulder blocking Uppingham Road,” she said.
Footage online showed police attempting to hold back crowds as objects including bottles were thrown.
A resident from Green Lane Road said what she witnessed on Saturday evening was “very intimidating”.
“The whole situation seemed really out of control,” she said.
“The police were there but it didn’t seem like they had a great handle on things.
“People were still feeling very scared, unsure and uncertain, and with everything else that’s gone on recently, there’s also a lot of tension building up in the few weeks that we’ve had this happen and unfold.”