Republican paramilitaries, either from the IRA or a splinter group, are suspected of carrying out a nail-bomb attack on the home of a Protestant family in north Belfast in the early hours of yesterday.
It had previously been reported that loyalists were responsible for the spate of pipe-bomb attacks.
More than 140 of the devices have been thrown at houses in Northern Ireland this summer.
However, it appears that a gang from the Catholic, working-class Ardoyne area was responsible for yesterday's attack on the home of the McCullough family in Westland Road.
The attack appeared a determined attempt to kill or injure members of a Protestant family.
Mr Gerald McCullough, his wife, Rosaleen, and their children, Dean (16), Jonathan (11) and Daryl (8), were asleep when a car pulled up in front their house at 3 a.m.
One of the gang threw a heavy lump of concrete at the front living-room window.
The point of first throwing the piece of concrete was to break the window so the following pipe-bomb could be thrown into the house.
However, the concrete failed to break the double-glazed, PVC-framed window.
The bomb, consisting of a metal tube packed with explosive and six-inch nails, was then thrown at the front of the house. It landed in the front garden but only partially exploded, causing no damage to the house.
Mr McCullough, who has lived in the Protestant Westland housing estate for most of his life, said his home was picked because it was the only house that had a light on at 3 a.m.
Ms McCullough works at night and was dozing on the sofa in the living-room when the attack happened.
She was awoken when the concrete hit the window and saw the flash as the bomb exploded.
Mr McCullough said: "They targeted us because the light was on. It was just an easy target. We're a wee bit shaken. The kids don't understand. If it had come in through the window my wife could have been killed or very seriously injured."
He pointed out that his youngest two sons sleep in the front double bedroom and they, too, were vulnerable to injury. The McCulloughs own their house, and Mr McMcCullough said he had no intention of leaving.
The attack follows another on a Catholic family home at Ingledale Park, a quiet residential street off Crumlin Road, between Ardoyne and the loyalist Glencairn area.
A pipe-bomb exploded in the front garden of the house, breaking the living-room and upstairs bedroom windows.
A man and his 12-year-old daughter were in the house. The rest of the family were away on holiday.
Ingledale Park is close to the Catholic primary school in the loyalist enclave of Glenbryn in Upper Ardoyne.
Residents in Ingledale said the street had always been religiously mixed.
More trouble is expected in the area when the school term resumes in just over a week.
Elsewhere yesterday, loyalists from the Lisburn area are believed to have carried out an arson attack on St Peter's Church, the Rock, at Stoneyford a few miles west of Belfast.
The arsonists broke into the church and started a fire in the pews at around midnight.
The fire was brought under control and the damage was contained.