The new unrest late Monday prompted a top police officer to issue a rare challenge to Northern Ireland's First Minister Peter Robinson and his deputy Martin McGuinness to condemn the violence publicly.
"I did not have a call from either of them in the run-up to this event and where are they today jointly speaking out against what has happened?"Assistant Chief Constable Alistair Finlay told BBC radio.
His comments came after dissident republicans threw petrol bombs, concrete slabs and bottles at Protestant Orangemen and their police escort marching through Ardoyne, a mainly Catholic area of northern Belfast.
Police responded with rubber bullets and water cannon in a bid to subdue the demonstrators.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Earlier, officers in body armour removed more than 100 people who staged a sit-down protest in the road.
Fifty-five officers have been injured in 48 hours of rioting in the British province.
The 28 new victims included a female officer who was hit with a breeze block, police said. She and another officer are still in hospital but none of their injuries were life-threatening, they added.
Rioting late Sunday and early Monday left 27 police injured, including three with gunshot wounds, officials said.
Finlay, of the Police Service of Northern Ireland, called for a permanent solution to the sensitive issue of the annual marching season, which remains a flashpoint despite the peace process in the province.
"This is the only way we can move away from the disorder, tensions and fear that grips Northern Ireland every year," he said. "Northern Ireland cannot afford to have violent images beamed across the world every summer -- images which are totally unrepresentative of the vast majority of people who have embraced a peaceful and vibrant future."
July 12 is the biggest day in Northern Ireland's marching season and sees Protestants mark Prince William of Orange's victory over the Catholic King James II at the Battle of the Boyne in 1690.
A local lawmaker blamed dissident republicans determined to wreck Northern Ireland's peace process for provoking the unrest, which he said came during what would otherwise have been a peaceful protest.
"All that was achieved by this was that it undermined local residents and prevented them holding their planned protest," said Gerry Kelly, a Belfast lawmaker from the republican, Catholic Sinn Fein party.
"But it is obvious by the small numbers involved that there was no mass mobilisation."
Another local lawmaker, Jimmy Spratt of the pro-British Protestant Democratic Unionists, told the BBC the violence had been "orchestrated by a very small number of people".
"I think a lot of progress has been made in terms of the violence we have seen in previous years," he said. Unrest also flared in other parts of Northern Ireland Monday.
Rioters tried unsuccessfully to set a Dublin-Belfast train alight at Lurgan, southwest of Belfast.
In the nationalist Bogside area of Londonderry, northwest of Belfast, a masked gunman fired five shots in the direction of security services but no-one was hurt.
Despite the relative calm in Northern Ireland since a peace agreement in 1998, violence frequently breaks out around July 12 as Catholics try to prevent the marches from going ahead.
