Arab satellite TV al-Jazeera has aired a video made by a previously unknown militant group, showing four Western nationals taken hostage in Iraq.
A Briton, two Canadians and a US citizen were kidnapped in western Baghdad on Saturday.
The video claimed they were undercover spies working as Christian peace activists, and showed the passport of the UK man, 74-year-old Norman Kember.
No demands or specific threats against their lives were made in the tape.
Mr Kember was shown sitting on the floor with three other men.
BBC security correspondent Gordon Corera says the hostages did not appear in distress and it seemed a positive sign that no gunmen were threatening them in the video, from the Swords of Truth Brigade.
It bears all the hallmarks of a political kidnapping, not one for money, our correspondent says.
The video showed what appeared to be Mr Kember's passport
The footage had a date stamp indicating it was recorded on 27 November.
A US-based group which says it is involved in violence-reduction programmes confirmed on Tuesday that four of its members had been seized in Baghdad.
Christian Peacemaker Teams (CPT) said its teams of trained peacemakers "work in areas of lethal conflict around the world."
The organisation said it had been present in Iraq since April 2003, "providing first-hand, independent reports from the region, working with detainees of both US and Iraqi forces, training others in non-violent intervention, and human rights documentation".
Canada says it is doing all it can to ensure the safe return of its nationals.
"I can assure Canadians that there is no more urgent priority than the safe return of our citizens," Prime Minister Paul Martin said.
The UK Foreign Office issued a statement "utterly condemning" the kidnapping and the video.
"The release of this video can only cause further distress to their families at this difficult time," a statement said.
A friend of Mr Kember, Pat Gaffney, told the BBC she was glad he has been shown to be still alive, but expressing anxiety about the future.
A German woman and her driver are also believed to have been kidnapped in Iraq in the last few days.
German TV station ARD says it has a video showing the woman and her driver, with kidnappers demanding Germany cut ties with the Iraqi government.
A group of Iranian pilgrims were also kidnapped in the town of Balad north of the Iraqi capital Baghdad.
Four men and two women were seized on a pilgrimage to a Shia Muslim shrine in Samarra. The women were released several hours later, police said.