The kidnapped British peace activist Norman Kember was shown in a new hostage video which has appeared on al-Jazeera television today.

The 25-second, silent videotape shows three of four hostage Christian Peacemaker activists, with a superimposed date stamp of February 28.

The four were kidnapped in Baghdad more than three months ago, on November 26. The recording says that the men asked their governments and countries in the Persian Gulf to work for their release.

The tape broadcast today showed the three men sitting in chairs and taking turns to speak, although there was no sound. Mr Kember has white hair and a slight beard, while the two others - believed to be the two Canadians, James Loney, 41, and Harmeet Singh Sooden, 32 - had dark hair and full beards. All appeared to be in good health.

The hostage apparently missing from the tape was the American - Tom Fox, 54, of Virginia. There was no mention of his whereabouts.

The four workers were last seen in a videotape dated January 21, which was aired by al-Jazeera a week later.

In that broadcast the al-Jazeera newsreader said that the hostage-takers had issued a statement saying it was the "last chance" for US and Iraqi authorities to "release all Iraqi prisoners in return of freeing the hostages otherwise their fate will be death". No deadline was set.

The previously unknown Swords of Righteousness Brigades claimed responsibility for the kidnapping.

A Foreign Office spokeswoman said: “We are concerned that only three of the four hostages are shown and will seek reassurance from the hostage-takers that all four are well.

“To release a video of this kind is obviously extremely distressing for the relatives, and our thoughts are with them, as well as with the victims who have now been held for more than 100 days. They are peace campaigners dedicated to helping other people, and should be freed immediately.”

Christian Peacemaker Teams (CPT), a Chicago-based group, has been working in Iraq since October 2002, investigating allegations of abuse against Iraqi detainees by American and Iraqi forces. Its teams host human rights conferences in conflict zones, promoting peaceful solutions.

In a statement, the CPT said: "In the latest video we were so glad to see Jim Loney alive. We were so glad to see Harmeet Sooden alive. We were so glad to see Norman Kember alive. We do not know what to make of Tom Fox’s absence from this video.

"We continue to pray for their safe and speedy release so that they may return to their families and carry on their peaceful work on behalf of all Iraqi detainees."

Muslim scholars and activists from around the world have appealed for the release of the aid workers, who are among more than 200 foreigners and thousands of Iraqis to have been kidnapped since the invasion of Iraq in 2003. Fifty-four foreign hostages are known to have been executed by their captors.

Also still held captive is Jill Carroll, an American reporter who is believed to be being held by the Islamic Army in Iraq, the insurgent group that freed two French journalists in 2004 after four months in captivity.

Bayan Jabr, an Iraqi interior ministry official who is in charge of Iraq’s police, says that he believes the 28-year-old freelance reporter for The Christian Science Monitor is still alive, although the deadline set by her captors for the US to meet their demands expired late last month.

Three videotapes provided by the kidnappers to Arab satellite television stations identified the group holding her as the previously unknown "Revenge Brigades." She was seized on January 7 in Baghdad and her translator was killed.

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