The UK government has condemned a videotape issued by the kidnappers of five British men held captive in Iraq.
A Foreign Office spokesman said the tape would "add to the distress of the men's families and friends".
In the film, dated 18 November, the kidnappers say they will kill one of the men as a "first warning" unless UK forces leave Iraq within 10 days.
The five men were seized on 29 May from Baghdad's finance ministry building by gunmen disguised as police officers.
They are being held by a militia group calling itself the Islamic Shia Resistance in Iraq.
The tape, which the Foreign Office is studying, is in Arabic and was broadcast on Al-Arabiya television on Tuesday.
The Britons - four guards and a computer expert - were initially taken to a Shia suburb after being seized.
Consular officials had remained in regular contact with the families of the men, the spokesman added.
The case has not featured in the media as much as other kidnappings in Iraq - including those of Ken Bigley and Margaret Hassan - because of a Foreign Office request for minimal coverage.
That request was made in keeping with the wishes of the men's families.
The Foreign Office says it does not want anything to get in the way of its negotiations, through third parties, to get the men released.
In the tape, filmed in front of an "Islamic Shia Resistance in Iraq" flag, one of the men gives his name, says he has been held for 173 days and adds: "I feel we have been forgotten."
In written text shown on the video, the kidnappers say the UK should "withdraw all the thieves and the gangs that they have brought with them to plunder and squander our wealth and resources, and to return what they have stolen".
They warn that, if the UK does not meet its demands, "this hostage will be executed on day number 10 as a first warning, then other details that you will not like will be made public".
It is unclear whether the 10-day deadline begins now, or when the recording was made.
The Foreign Office spokesman said: "No matter what the cause, hostage-taking can never be justified.
"We again call on those holding the men to release them unconditionally."
Prime Minister Gordon Brown's spokesman also condemned the release of the videotape.
"It's our long-established policy not to comment on such footage and we encourage others not to speculate," he added.
"That would be unhelpful and distressing to the families concerned."
BBC special correspondent Gavin Hewitt said a crucial difference between this kidnapping and previous cases had been that intelligence agencies believed the Britons were being held by a splinter group of the Mahdi army - a Shia militia - rather than Sunnis linked to al-Qaeda.
But the "secretive cell" did not appear to be part of a big organisation, BBC security correspondent Frank Gardner said, which made it more difficult for British authorities to understand its motives.
However, our correspondent said going public with the tape signalled a change of behaviour in the kidnappers as, up until now, nothing had been heard from the five men being held.
It was putting "immense pressure" on the British government to resolve the issue, but little was yet known about the hostages' whereabouts and how serious the group's threats were, he added.
In September, the families of the five men urged their captors to end their "torment" of being separated from "ordinary family men".
The statement continued: "They are sons, fathers and brothers who were working to support us - their families.
"We miss them so much and want them to come home to us so that our families can be complete again and our children no longer have to endure the pain of missing their fathers."