"Help me please help me, these might be my last hours," said a weeping Hassan in a videotape broadcast on the Qatari al-Jazeera TV station.
Hassan, the head of CARE International operations in Iraq, was seized Tuesday but no group claimed responsibility for her kidnapping.
She begged the British people to help her escape the fate of Ken Bigley, the British hostage who was beheaded by the Jihad and Tawheed earlier this month.
"I beg of you, the British people, to help me. I don't want to die like Bigley," she said.
She pleaded with Blair to pull out the British troops from Iraq "and not to send them to Baghdad, because that is the reason why people like me and Bigley are being kidnapped and might die."