Outbreaks of gang violence in Penwortham and Preston are being fuelled by social media apps WhatsApp and Snapchat, say police.
Parents are being urged to keep a close eye on their children's online activity after a recent escalation in gang violence in Penwortham and Preston.
It follows an admission by a Lancashire Police chief that the escalating gang violence cannot be tackled by police alone.
Updating residents on Tuesday's violent disorder in Penwortham, Chief Inspector Gary Crowe said that "thuggish, violent behaviour" will not be tolerated.
But the police chief conceded that such incidents can only be stopped with the pro-active help of parents, schools and social services.
The police chief said recent outbreaks of gang violence, including armed confrontations at Runshaw College in Leyland and Liverpool Road in Penwortham, had been arranged by young people using popular social media apps WhatsApp and Snapchat.
He said the apps are being used to arrange fights between rival youths from different schools. The location and terms of the fights are then widely shared by young people who are invited to attend the fight as a spectator.
Ch Insp Crowe said: "We know that the altercation between two groups on Liverpool Road on Tuesday, March 26 has caused concern amongst lots of residents and businesses who witnessed it, in particular schoolchildren who were in the area at the time.
"It involved a group of rival youths who are known to each other and had met up for a pre-arranged fight.
"We cannot tackle the issue of rival youths and any potential subsequent disruption alone; we are working closely with education services and children’s social care to look at a way forward in conjunction with schools.
"I would also encourage parents to think about what their child or children are up to on social media as yesterday’s fight and other incidents have been fuelled and discussed on WhatsApp and Snapchat."
The police chief confirmed that the incident on Tuesday, which allegedly involved a machete and a baseball bat, had been a "targeted attack" on a rival gang member.
He also moved to reassure people that the ongoing rivalry between armed gangs in Penwortham does not pose a threat to the wider public.
"Our officers were already in the area due to previous issues with youths which we are aware of", said the chief inspector.
"Thankfully we dealt with the disorder before anyone got seriously hurt and arrested four people, who remain in police custody.
"There was and is not any on-going wider threat to the public and for this reason, I would urge you to go about your daily business as usual."
He added: "We will continue to have officers patrolling Penwortham, both on foot and from Mounted, which will include school areas.
"This is to make you feel safe and reassured, and isn’t in response to any specific intelligence.
"We will also be monitoring the area and let me be clear, we will not tolerate thuggish, violent behaviour like we saw yesterday.
"We have been visiting shops and businesses along Liverpool Road as part of our enquiries and to offer some reassurance.
"If you have any concerns, please feel free to speak to one of our officers out and about."
If you have any information about Tuesday's incident or the issue of youth/gang rivalry in the area, please call us on 101 quoting log 915 of March 26.
Alternatively independent charity Crimestoppers can be contacted anonymously on 0800 555111