John Desmond Doherty, 51, was asleep in bed in a house in Belfast when he was shot in the head and died instantly. The loyalist Ulster Freedom Fighters later claimed responsibility.
The second victim, later named as Cormac McDermott, an electrician in his 30s, was shot dead in Ballymena, Co Antrim. A woman, believed to be his wife, was admitted to hospital with gunshot wounds.
The third man was shot dead at the High Trees garage in Donaghadee, Co Down.
In Londonderry, a man was seriously injured in a mortar bomb explosion in the town centre.
Firebomb explosions at three central London stores yesterday, said by Scotland Yard to be the work of the IRA, were the first terrorist bombs to explode in Britain since the Downing Street declaration in December, writes James Cusick.
The message appears to be that the terrorist campaign, although scaled down in both Britain and Northern Ireland, is not over. The Oxford Street stores of Mothercare, C & A, and a small independent luggage store, were all damaged by fire as incendiary devices exploded in the early hours of yesterday morning.
Scotland Yard said it had received no specific warning of the attacks, but Sally Collinson, of the Oxford Street Association, said stores had received warnings a couple of days ago.
After forensic science examination, a Scotland Yard spokeswoman said the fires had been caused by devices 'clearly attributable to the Provisional IRA'.
The devices, in stores within 400 yards of each other, exploded in succession beginning at 3.25am. The Mothercare and C&A stores incurred only minor damage.
A C&A spokesman said the device had been concealed in a clothing area. The luggage store sustained greater damage. There were no injuries.