Shots were reported to have been fired in Lurgan last night as trouble flared in the Co Armagh town.
Violence erupted just hours after Justice Minister David Ford met with local representatives in the Kilwilkie area yesterday afternoon.
It is understood to be linked to the arrest of Republican Sinn Fein president Des Dalton.
He was lifted by police in Lurgan last night. The party claims it follows his attendance at a parade in support of republican prisoners in Lurgan in January.
Police received reports that two shots were fired after a number of cars were hijacked and set alight, it was reported.
The PSNI also examined a suspicious vehicle parked at Lake Street in the town which forced the closure of the Belfast to Dublin railway line last night.
Local SDLP Assemblywoman Dolores Kelly, who met with minister Ford yesterday, condemned last night's violence.
She said: "I condemn the violence. It's long past the time these people are brought before the courts and sentenced."