A British Muslim group has appealed for the safe release of Norman Kember and three other peace campaigners taken hostage with him in Iraq in November.
Norman Kember has been shown blindfolded and shackled
The appeal, from the Muslim Association of Britain, was broadcast on al-Jazeera TV channel in Arabic and followed media appeals from the 74-year-old's family.
The men remain missing two weeks after their captors threatened to kill them.
The Swords of Truth group demanded all Iraqis detained by coalition forces be freed by 10 December - a call not met.
Mr Kember, from Pinner, north London, was seized in Baghdad on 26 November.
He was taken captive along with Canadians James Loney, 41, and Harmeet Singh Sooden, 32, and an American Tom Fox, 54.
Mr Kember was last seen in a video aired on al-Jazeera on 8 December, blindfolded and with his hands tied.
Dr Tamimi was interviewed on al-Jazeera TV
He had travelled to Iraq as a gesture of solidarity with Christian Peacemaker team - a Canadian-based international peace group.
The Muslim Association of Britain representative Dr Azzam Tamimi said in his Christmas Eve appeal broadcast after 1800 GMT that the hostages were "friends of the Iraqi people".
"They opposed the war on Iraq and the invasion from the beginning," he said.
"We said and say again to those who are holding them that the best way to serve the Iraqi cause is to release these people during this period - Christmas and the new year."
Dr Tamimi said after the broadcast that he believed the hostage-takers would want to release the men, but were held back by "practical difficulties".
"Perhaps someone in Iraq, some other parties, need to work together to co-operate somehow to facilitate this release."
Meanwhile, in a joint advert to appear in papers and on radio in Iraq over the new few days, the hostages' families have called for the safe return of their relatives.
In the advert the families say: "A month has passed since our loved ones - Norman, James, Harmeet and Tom - were kidnapped in Iraq.
TIMELINE OF ABDUCTION
26 November: Norman Kember is reportedly abducted along with three other peace workers
30 November: A video showing the captured peace workers is shown by the previously unknown militant group Swords of Truth Brigade
1 December: Anti-war campaigner Anas Altikriti flies to Iraq to plead for Mr Kember's life
4 December: Mr Kember's wife Patricia makes a plea for her husband
11 December: The original deadline from Mr Kember's captors passes
"Many clerics and religious figures from the Arab and Muslim world have spoken over the past weeks of the good work they were doing in Iraq and that their organisation have done in Palestine, and they have called for their release.
"We appeal to you to help us ensure the safe return of our relatives.
"If you have any information which can help, please call this number. You do not have to reveal your identity."
A telephone number and e-mail address have been set up in the hope the kidnappers will make contact.
The Reverend Alan Betteridge, who is a friend of Mr Kember, said he hoped the group holding the men would respond to the appeal.
"I do hope that at this time of the year as in the Christian world we think of peace and goodwill, that that same idea will come across to all the people involved in this.
"That they will see the message from the family, recognise the genuineness of these people and release them because they are good for the world, the world needs them, we need them."