Jaffna is the heartland of Sri Lanka's Tamil minority and was the epicentre of the long separatist war that ended in 2009.
Tensions persist between troops deployed in the area and the local Tamil population, and last year the government accused the military of backing a gang terrorising civilians in the area.
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On Friday Law and Order Minister Sagala Ratnayaka said authorities were grappling with a fresh wave of gang-related violence, but denied it was related to last year's unrest.
He said eight people had been seriously wounded in two days in Jaffna, which lies 400 kilometres (250 miles) north of Colombo, in what appeared to be an extortion racket.
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"We have already arrested six people from this new gang and we are looking for several others," he said.
The current government came to power in January 2015 promising reconciliation after the decades-long war and has tried to restrict military involvement in day-to-day activities in Jaffna.
However, civil society groups say elements loyal to the former administration are still in key positions and are fomenting unrest.
Government forces maintain a large presence in the former war zone and keep a close watch on the Tamil population, eight years after the end of the war.
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