New footage of Briton Norman Kember and three other Westerners held hostage in Iraq has been aired on Arab TV.
Norman Kember in the latest video
Mr Kember, 74, of Pinner, north London, was seized with two Canadians and an American on 26 November and was last seen in a video seven weeks ago.
The new video, aired on al-Jazeera TV, includes a message from the group, which calls itself the Swords of Truth, demanding all Iraqi prisoners be freed.
It says the four hostages will be killed if its demands are not met.
The tape shows the four hostages standing against a wall and is dated 21 January.
The men appear to be speaking to the camera but their words are not audible.
Mr Kember's fellow captives are Canadians James Loney, 41, and Harmeet Singh Sooden, 32, and American Tom Fox, 54.
Al-Jazeera said it had aired the whole of the recording, which was about 55 seconds long.
'Kind of breakthrough'
The Qatar-based satellite channel declined to reveal how it got hold of the tape.
A message on the tape demanded the US and Iraqi authorities release all their Iraqi prisoners.
TIMELINE OF ABDUCTION
26 November: Norman Kember abducted along with three other peace workers
30 November: Video footage of the hostages aired on al-Jazeera
2 December: Second video of the hostages aired. Their captors threaten to kill them unless their demands are met by 8 December
8 December: Third video is aired on al-Jazeera showing Mr Kember and US hostage Tom Fox wearing orange jumpsuits, blindfolded and shackled. The captors' deadline is extended to 10 December
28 January: New video of hostages, dated 21 January, aired on al-Jazeera
The British Embassy in Baghdad said it was assessing the video of the hostages.
In a statement, it said: "After so long without word it is a relief that the video shows them alive. We continue to urge those holding them to release them."
Anas Altikriti of the Muslim Association of Britain, who has been campaigning in the Middle East for Mr Kember's release, said the video showed there had been "some kind of breakthrough" in the efforts to communicate with the captors.
He said he still did not know who was holding the men or where they were, but the video was a positive sign that they were still being held by the same group.
But BBC correspondent Nicholas Witchell, in Baghdad, said it was "disturbing" that the group was still making political demands which could not be met.
He said the US had released 420 prisoners, including five women, two days ago but there were many thousands of people still in detention.
The Reverend Alan Betteridge, said he was pleased to see his friend Mr Kember was still alive but was concerned the kidnappers were still making the same demands "couched in these threatening terms".
He said: "I had thought with all the pressure put on them from the Muslim world they would have found a way of releasing them without making these sorts of threats."
Mr Kember's wife, Pat, was "coping very bravely and strongly", he added.
James Loney is one of two Canadians held hostage
Mr Kember, a retired professor, was last seen in a video aired on al-Jazeera in early December, blindfolded and with his hands tied.
The Swords of Truth group had threatened to kill the hostages by 8 December unless Iraqi prisoners were released.
The deadline was then extended by two days and expired on 10 December. There had been no news of the hostages since then.
The group had travelled to Iraq with Canadian-based international peace group Christian Peacemaker Teams as a "gesture of solidarity".