Political leaders have condemned the apparent murder of aid worker Margaret Hassan by her kidnappers in Iraq.
Tony Blair said it was "abhorrent", while Irish premier Bertie Ahern said her kidnappers "stand condemned by... the entire international community".
Mrs Hassan's husband has begged for the return of the body of his Irish-born wife, who had UK and Iraqi nationality.
A video showing a blindfolded woman being shot in the head has surfaced and has been checked by experts.
UK Foreign Secretary Jack Straw said they had concluded Mrs Hassan had "probably" been murdered.
He added: "To kidnap and kill anyone is inexcusable.
"But it is repugnant to commit such a crime against a woman who has spent most of her life working for the good of the people of Iraq."
Mrs Hassan, 59, had lived in Iraq for 30 years.
She was seized by an unknown group in the Iraqi capital on 19 October.
Arabic TV news channel Al-Jazeera said on Tuesday it had had a copy of the videotape showing Mrs Hassan's apparent killing for several days, but had chosen not to broadcast it.
Appeal to kidnappers
Mrs Hassan's husband Tahseen has appealed to the kidnappers to tell him the whereabouts of his wife's body.
He said: "They can tell me. They can call the helpline. I need her. I need her back to rest in peace."
Mrs Hassan's sisters and brother, Deirdre and Kathryn - who live in London - and Geraldine and Michael Fitzsimons, said in a statement their "hearts are broken".
Mr Hassan made an emotional plea for her body to be returned
They said: "We have kept hoping for as long as we could, but we now have to accept that Margaret has probably gone and at last her suffering has ended."
On Thursday morning a special church service for Mrs Hassan was held in Kenmare, County Kerry, the area where her mother was born and her sister Geraldine lives.
After Mrs Hassan was kidnapped, her family and colleagues repeatedly pleaded for her release.
During prime minister's question time in the Commons, Mr Blair paid tribute to Mrs Hassan and expressed his condolences to the family.
Conservative leader Michael Howard told MPs that Mrs Hassan's probable murder "shows we are up against barbaric terrorists who want to destroy Iraq's future - we must stand steadfast".
'Violation' of values
The Archbishop of Westminster, Cardinal Cormac Murphy-O'Connor, said her presumed death was "a violation of the most basic value of Muslim mercy".
The Muslim Council of Britain also expressed its condemnation saying: "Mrs Hassan had served the Iraqi people tirelessly for most of her adult life and it is appalling her goodness has been repaid with murder. "
Mrs Hassan was driving to her job as director of Care International's Iraq operations when she was seized. The agency has since halted work in the country.
Sir Harold Walker, former British ambassador to Iraq and former chairman of the board of Care International, told the BBC Mrs Hassan did "superb work" in Iraq and was one of his "heroines".
Sir Harold said he believed her kidnappers wanted to show that Iraq was ungovernable in its current state.
Mrs Hassan was filmed by her captors asking Tony Blair to pull British troops out of Iraq.
If Mrs Hassan's death is confirmed, she will be the first foreign female hostage to have been murdered in Iraq.
The only other western woman to known to be currently held in Iraq is Teresa Borcz Khalifa, 54, a Polish-born long-time resident of Iraq who was seized last month.
The body of a woman, believed to be a westerner, was found in Falluja on Sunday, but has not been identified.