Sixteen police officers were injured in rioting in Belfast in the wake of the Twelfth of July Orange Order parades.
Fourteen people have so far been arrested in relation to the disorder at the notorious Ardoyne flashpoint in the north of the city and in the nationalist Markets area in the south, police announced.
A further 12 people were detained in connection with rioting in Londonderry.
None of the officers suffered life-threatening injuries, with most receiving limb wounds or concussion.
It was the second successive night police were targeted, with 22 officers injured when violence broke out on Monday night in the nationalist areas of Broadway, Old Park and North Queen Street in the west of Belfast.
The violence directed towards police over the last 48 hours has emanated from mainly republican areas.
Last night petrol bombs, bricks, bottles and fireworks were hurled at officers and cars were set alight in the Ardoyne, which has a history of sectarian clashes.
In response, police in riot gear fired around 55 baton rounds and high-powered water cannon at crowds of around 200 to 300 mainly young people in the Estoril Park and Brompton Park areas.
Some officers were set alight briefly when hit by petrol bombs and targeted by lasers, while a local photographer was hit by a baton round.
Nine people - eight males and a female - were arrested following disorder in the Ardoyne area.
Five, including the woman, have been charged with riotous behaviour, a 12-year-old boy has been reported to the Public Prosecution Service (PPS) and the three other men remained in custody.
Five people were arrested on suspicion of riotous behaviour in the Stewart Street area of the Markets. All remained in custody.
In Derry there were 12 arrests (11 males, 1 female) following the disorder - two remained in custody, four have been released on bail pending further inquiries and six were released pending reports to the PPS.
Assistant Chief Constable Alistair Finlay condemned the disorder, which he said had been confined to very small pockets across Northern Ireland.
"The vast area of Northern Ireland was extremely peaceful, yet for these few streets we get headlines of violence, of people injured, of communities and relationships being broken, and infrastructure and property damaged," he said.
"What we saw was the release of built-up energy, a group of young men engaging in thug-like behaviour, and they will be brought to justice. There will be a follow up operation like last year and people will be brought before the courts.
"It is hugely regrettable that we get to this situation each year. There are a large number of people across community groups, government and faith groups doing a huge amount to reduce the impact and change things for the better. We all need to redouble these efforts and sustain them to get a real and meaningful change for residents of these areas. That is the very least they need and deserve."
Away from Belfast and Londonderry, Armagh City and Ballymena, Co Antrim, also experienced public disorder last night.
There were also disturbances in Newry, Co Down, when youths threw stones and set tyres on fire.
In Londonderry, crowds gathered and a van was set ablaze on a flyover close to Free Derry Corner.
Yesterday's Twelfth of July celebrations by Orangemen involved tens of thousands of members of the loyal orders walking the streets to commemorate the 1690 Battle of the Boyne victory of Protestant King William of Orange over Catholic King James II.