The British and Irish prime ministers have insisted they will not let the murder of a former Sinn Fein man derail the peace process in Northern Ireland.
Tony Blair and Bertie Ahern were speaking after Denis Donaldson, a former British agent, was found shot dead in the Irish Republic.
Few details of the killing have been released, but it is known that he had been shot in the head and in the arm.
The IRA said it had "no involvement whatsoever" in the murder.
Mr Donaldson, 56, was found dead at his remote home, near the village of Glenties in County Donegal, at about 1700 BST on Tuesday.
It is understood that Irish police found two shotgun cartridges close to his body.
He had been expelled from Sinn Fein in 2005 after admitting he was a paid British spy.
An Irish police officer cordons off the murder scene
Irish police have begun detailed searches of the area. They are expected to release further information about the murder later on Wednesday.
Members of the Garda Technical Bureau are due to arrive at the scene later on Wednesday, whilst a special incident room has been set up in the local station, from where the investigation is being co-ordinated.
The republic's state pathologist, Dr Marie Cassidy, is in Glenties and is expected to carry out a preliminary examination in the cottage where Mr Donaldson was found.
His death came two days before a planned visit to Northern Ireland by Mr Blair and Mr Ahern to unveil their blueprint for reviving the assembly at Stormont.
Northern Ireland Secretary Peter Hain said the two prime ministers would still press ahead with their plans on Thursday, as the murder could not be used "as an excuse to be deflected from that process".
"If we were to allow the peace process to be derailed we'd be giving into violence, in this case a grisly, gruesome murder, perhaps deliberately calculated to throw a spanner in the works and make the political process difficult," he said.
"We're not going to allow that to happen."
TIMETABLE OF EVENTS
4 October 2002: Three men including Mr Donaldson arrested following raid on Sinn Fein's Stormont office. Power-sharing executive collapses and government restores direct rule to NI a week later
8 December 2005: Charges against three men dropped "in the public interest"
16 December 2005: Sinn Fein says Mr Donaldson was a "British agent" and expels him from the party: he later says he worked as a spy since the 1980s
Government and police reject the party's claim raid was politically motivated
4 April 2006: Donaldson found shot dead in County Donegal
An Irish government official said police were making "every effort" to find the killers.
Sinn Fein leader Gerry Adams said he wanted to "disassociate (his party) and all republicans who support the peace process from this killing".
A Downing Street spokesman said Mr Blair "strongly condemned" the killing and had noted Mr Adams' statement of condemnation.
Irish Prime Minister Bertie Ahern described the death as a "brutal murder".
Mr Donaldson moved out of his Belfast home last December, and had been living in the run-down cottage which had neither electricity nor running water.
Hugh Jordan, chief reporter of the Sunday World newspaper, interviewed Mr Donaldson last month, after tracking him down.
He said that when he spoke to him he had "the sort of look of a hunted animal, but after a while he settled down".
"I did ask him about his future and ask him what the future held for him now and he said 'this is it' and I said 'Donegal?' and he said 'yes'.
"I asked him would he ever go back to Belfast and he said 'I don't know'.
"But he did not appear to be a man who was overly worried about his safety or security at that stage."
Mr Donaldson had been Sinn Fein's head of administration at Stormont before his 2002 arrest over alleged spying led to its collapse.
Mr Donaldson and two others were acquitted of charges last December "in the public interest".
One week later he admitted being recruited in the 1980s as a paid British agent.
He said there had not been a republican spy ring at Stormont.