Aid agency Care International has made a televised appeal asking the kidnappers of its Iraq director Margaret Hassan to release her.
Margaret Hassan urged Tony Blair to withdraw forces from Iraq
Secretary-general Denis Caillaux asked them "to understand she is an Iraqi" and called for her immediate release.
Mrs Hassan, who was seized on Tuesday, has dual Iraqi and British citizenship and has lived in Iraq for 30 years.
A video was released on Friday showing her begging Tony Blair to withdraw British forces to save her life.
It is still not known which group has kidnapped Mrs Hassan, as unusually there was no banner or insignia on the video, nor any claim of responsibility.
Those working to free Dublin-born Mrs Hassan, who is in her 60s, are stressing that she has not been connected with Britain for decades.
"Mrs Hassan is a humanitarian who has lived in Iraq for 30 years and has worked for the past 13 years to secure better health and water and sanitation for the people of Iraq," Mr Caillaux said on al-Jazeera television.
"She is a naturalised Iraqi citizen and always holds the people of Iraq in her heart.
"Care joins with many of the people whose lives Mrs Hassan has touched over her decades of service in Iraq in reaching out to her captors to appeal to their humanity."
He said the agency was deeply concerned for her welfare.
"We call on the people who are holding Mrs Hassan to understand that she is an Iraqi and to release her to her family and the people who love her."
Numerous appeals have been made from within Iraq for Mrs Hassan to be freed unharmed.
Her Iraqi husband Tahseen Ali Hassan said: "My wife is apolitical, she is a humanitarian worker and I ask you to release her."
Care International has suspended its aid operations in Iraq following her kidnapping.
Al-Jazeera had earlier broadcast a video showing Mrs Hassan sobbing and pleading to be saved from the same fate as murdered British hostage Ken Bigley.
In the footage, Mrs Hassan said: "Please help me. The British people, tell Mr Blair to take the troops out of Iraq and not bring them here to Baghdad.
"That's why people like myself and Mr Bigley are abducted, and we might die."
Downing Street made no response to the video.
Freelance journalist Felicity Arbuthnot, a close friend of Mrs Hassan, told the BBC: "She is a very tough lady and if she is crying on this video - I haven't been able to steel myself to look at it yet - that is really bad."
She added: "This is a woman who is frightened of nothing."
Mrs Hassan's plea follows Defence Secretary Geoff Hoon's announcement that 500 Black Watch soldiers and 350 support personnel will move from Basra to the US sector in central Iraq.
Terry Waite, who was held hostage in Beirut for five years, said he was with Mr Bigley's family trying to come to terms with his death when news of Mrs Hassan's capture came through.
He told BBC Radio 4's Today programme he was "appalled" by the kidnapping, but said he had feared using force to remove a dictator would create a power vacuum into which extremists would flood.