Prime Minister Gordon Brown has said the Government would do "everything in our power" to secure the release of British hostages being held in Iraq.
Concern about the five men's plight was heightened after the release on Saturday of a video from their captors claiming one of them had killed himself.
The message, which has not been independently verified, was condemned as "abhorrent" by the Prime Minister, who called for the men's immediate and unconditional release.
The video, from a group calling itself Shi'ite Islamic Resistance in Iraq, provides no proof of the death of the hostage, known only as Jason, and said that if the British Government wanted evidence it must open negotiations with the kidnappers.
In a harrowing taped message another hostage, understood to be a married father-of-two from Scotland called Alan, urged the Government to take action to secure his release.
Looking pale and drawn, Alan said: "Physically, I'm not doing well. Psychologically, I'm doing a lot worse. I want to see my family again. I would like for the British Government to please hurry. Please hurry and try and get this resolved as soon as possible."
Mr Brown raised the case with Iraqi Prime Minister Nouri Maliki in Baghdad on Saturday, and later said he had also discussed the men's plight with the Americans, who control the Iraqi capital where the men were seized in May last year.
Speaking during a visit in Israel, he said: "This abhorrent film will only add to the anguish of families who have suffered a great deal over a year for their loved ones who have been kept in captivity. I call on the hostage takers to release these people who have been held in captivity immediately.
"I will work with the Iraqi government, as I said to Prime Minister Maliki yesterday, to secure their release, and we will do everything in our power to work with everyone who is in a position to help us release these hostages. These men have suffered enough."
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The five men - an IT consultant named Peter Moore and four bodyguards whose identities have not been confirmed - were seized in May last year from the Iraqi finance ministry by a Shi'ite group who are demanding the release of nine prisoners detained by UK forces in southern Iraq.
