Security sources have been quoted as saying that an explosive device was responsible for a blast in a republican area of west Belfast which badly injured a father and son.
A 36-year-old man has been arrested in connection with the explosion.
The blast was at the back of a house in Glenalina Crescent in Ballymurphy yesterday.
The son, who is in his 30s, was found bleeding heavily and slipping in and out of consciousness. He had leg and head injuries.
His father, who is in his 50s, also had head injuries.
His wife later told a Catholic priest her husband and son had been clearing the shed at the time. They both underwent emergency treatment at the Royal Victoria Hospital, where their condition was described as "ill but stable". Their injuries are not life-threatening.
Initially there was speculation that the explosion was due to a gas leak. However, RUC sources were later quoted as saying it had been caused by an explosive device and gas workers on the scene could not find any leak.
A police spokesman said detectives planned to talk to the men.
An Orange Order march is due to take place on nearby Springfield Road on Saturday.
There is a growing dissident republican presence in Belfast. Both the "Real IRA" and Continuity IRA have expanded in the city in recent months, particularly in north and west Belfast.
The explosion followed the Ulster Freedom Fighters' threat to end its ceasefire but there is not believed to be a link. A neighbour said the father, who it is understood recently had a triple heart bypass operation, was carried out by ambulance men.
"He had blood all over his face. The son was taken out through the front door. He was bandaged and had blood dripping out of his socks," she said.
The woman, who declined to be named, expressed her shock at the blast. "It was so loud it rattled the windows and then neighbours phoned for an ambulance."
British army technical officers were last night still examining the scene of the explosion. Police there would not disclose details of its cause.
Father Denis McKinley, who spoke to the injured man's wife, said: "She told me the men were in the back garden. They were clearing something from the shed, or something like that, and the next thing she heard was the explosion.
"There was some rumour that one of them lifted a pipe, but it is all a bit garbled at this stage and nobody really knows exactly what happened."
Republican dissidents have been involved in a series of failed bomb attacks this year.
On Monday a partially-exploded device was found in a field close to Hillsborough Castle, Co Down, the residence of the Northern Secretary, Mr Peter Mandelson.
It is believed to have been lying there for some time, close to a perimeter wall, but outside a security fence protecting the grounds of the Hillsborough estate.