The former Sinn Féin official Denis Donaldson has been "brutally murdered" at his home in Co Donegal this evening.
Gardai were called to Donaldson's house in the village of Glenties, Co Donegal shortly at 5pm today where his body was found. It is understood that he was shot dead.
Mr Donaldson was expelled from Sinn Féin last December after admitting he had been a paid British spy for 20 years.
A one line statement from the IRA this evening said the organisation had "no involvement whatsoever" in Donaldson's death.
The Minister for Justice Mr McDowell said he was shocked by the murder and that it would cause mutual suspicion across the Northern Ireland parties.
Mr McDowell said Donaldson's body was found lying on the floor of the house he was living in in Glenties with a gun shot wound to the head. He also confirmed that Donaldson's right forearm was almost severed.
"Gardai are working on the theory that it is not a suicide, it is a homicide", Mr McDowell said this evening.
Minister for Justice Michael McDowell
The Taoiseach Mr Ahern condemned "this brutal murder" and said the matter was now being investigated by An Garda Siochana.
Mr Ahern added that he hoped those responsible for "this callous act will be brought to justice as soon as possible".
Downing Street said that Mr Blair "strongly condemned" the killing. A British government spokesman noted that Mr Adams had also condemned the murder and had disassociated what he called "pro-peace process republicans" from the attack.
Sinn Féin President Gerry Adams condemned the killing, saying he wanted to disassociate Sinn Féin and all republicans who support the peace process from the murder.
The Northern Ireland Secretary Peter Hain said he was "completely appalled by this barbaric act."
DUP MP Jeffrey Donaldson said the killing comes at a particularly sensitive time. "Particularly on the eve of the British and Irish governments declaring their position on the way forward."
"I think this will seriously undermine public confidence in the IRA and what they are about if it is proven to be the case that they are responsible for this murder."
Donaldson had moved out of his Belfast home and was been living in a run-down cottage without electricity or running water near Glenties.