The curfew, imposed late on Thursday on the entire Jaffna Peninsula, the home of most of the island's 3.2 million Tamils, was expected to be lifted later on Friday, said police spokesman Reins Pourer.
The violence was sparked on Thursday when a soldier's gun accidentally discharged while he was trying to get a haircut at a barber shop just outside the town of Jaffna, 300km north of the capital Colombo, police said.
The bullet killed an employee, and the soldier was arrested.
Furious residents on Thursday burnt tires, stoned military vehicles and seized police Superintendent Charles Wijewardene, who arrived to investigate the incident.
His body was later found lying on the street, covered with stab wounds.
He was the most senior police officer to be killed since the government and Tamil rebels signed a ceasefire three years ago.
Sri Lanka's police top brass flew to Jaffna on Friday to review the situation.
Residents contacted by telephone said the area remained tense.
Jaffna is the scene of two decades of fighting between government troops and Tamil Tiger rebels.