Police are warning against vigilantism after disturbances in Avenham on Sunday evening left an Asian youth stabbed.
More than 100 police were drafted in to deal with stone throwing youths who attacked cars around Clarendon Street as worshippers attended the Jamea Masjid mosque.
Police believe the trouble was between two criminal gangs which flared up as people left the mosque.
Preston's senior police officer, Chief Superintendent Mike Barton, said: "We believe that people have been moving in the hierarchy of drugs supply with a number of competing for the same area.
"Most of the activity is unknown to law-abiding members of the community, but it has spilled over into the lives of decent people."
The incident has raised questions of the community's trust in the police.
Yesterday uniformed officers were delivering letters of reassurance to all households in Avenham.
In the letter, Chief Supt Barton warns that any vigilante action in the area would be dealt with severely.
He said: "I can understand why some sections of the community feel like taking the law into their own hands. Many people have told me that they simply wish to protect their community.
"My appeal to those people is that you can best protect your community by supplying information to the police not by arming yourselves and patrolling the streets vigilante style. People who over react in that way and commit criminal acts will leave themselves open to being arrested and where necessary prosecuted."
Community leaders, including the police, local councillors, the chief executive of Preston City Council and MP Mark Hendrick met on Monday. They issued a joint statement: "The meeting discussed recent events and the grave concerns of the community were put before the police and the city council in forthright terms.
"They promised increased resources to deal urgently with these problems, caused by a handful of thugs, who have been terrorising the entire community in the Avenham area.
"This area has traditionally been a well integrated, diverse and harmonious part of the city.
"We have all resolved to keep it that way." Police say they will use anti-social behaviour orders against the small hardcore of thugs' who started the violence.