The Arab satellite television network Al-Jazeera said yesterday it had received several days ago a videotape of a blindfolded woman being shot, though it was not certain that woman was Hassan.
Al-Jazeera did not broadcast the video.
Hassan worked in Iraq for 30 years and was married to an Iraqi national. Irish-born, she held dual British and Iraqi nationality. Her family in Britain has already released a statement saying their hearts are "broken" at the news.
Hassan, 59, spent much of her life helping the Iraqi people. When she was abducted last month on her way to work, the executive director of CARE International's operations in Iraq had worked in the country for some 30 years.
"I need her. I need her back to rest in peace. Margaret lived with me in Iraq for 30 years. She dedicated her life to serving the Iraqi people. Please now, please return her to me." -- Tahsin Hassan
Following her abduction on 19 October, her kidnappers released several videos of Hassan pleading for British officials to remove the country's troops from Iraq and calling for the release of all female Iraqi prisoners.
Hassan's abductors threatened to turn her over to the group led by Jordanian-born militant Abu Mus'ab al-Zarqawi unless British troops left Iraq.
After the news of the video appearing to show her death was made public, Hassan's grief-stricken Iraqi husband Tahsin Hassan appealed to his wife's captors to give some word of where she could be found, even if only to bury the body.
"I need her. I need her back to rest in peace. Margaret lived with me in Iraq for 30 years. She dedicated her life to serving the Iraqi people. Please now, please return her to me," Tahsin Hassan said.
No group has claimed responsibility for her kidnapping or murder.
CARE, for whom Margaret Hassan worked for more than 12 years, released a statement yesterday saying it was with "profound sadness that we have learned of the existence of a video in which it appears that our colleague Margaret Hassan has been killed."
The organization added it was "shocked and appalled that this has been the apparent outcome of her abduction."
British Prime Minister Tony Blair said in a statement today that he shared the "abhorrence at the cruel treatment of someone who devoted so many years of her life to helping the people of Iraq."
Irish leader Bertie Ahern said he could not even begin to imagine the anxiety Hassan's family was experiencing and said those responsible for abducting Margaret stand condemned by everyone throughout the international community.
Though no one has yet confirmed that Hassan is the woman in the videotape, her family in Britain appears resigned to the fact that she is dead.
More than 170 foreigners have been kidnapped in Iraq this year. If Hassan's death is confirmed, she will be the first female hostage to have been executed.