It was not immediately clear which of the four hostages, who disappeared on 26 November, was not in the video broadcast on Tuesday by Aljazeera. It carried a 28 February date superimposed on the tape.
The tape showed the three men sitting in chairs. One of those on the tape had white hair and a slight beard, the two others had dark hair and full beards.
The previously unknown Swords of Righteousness Brigades had said they were responsible for the kidnapping.
The four workers - two Canadians, an American and a Briton - were last seen in a videotape aired by Aljazeera on 28 January and dated 21 January.
Until Tuesday, there had been no further word on the fate of Canadians James Loney, 41, and Harmeet Singh Sooden, 32; Tom Fox, 54, of Virginia; and Norman Kember, 74, of London.
Christian Peacemaker Teams, a Chicago-based organisation, 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 other developments, armed men on Tuesday morning ambushed a police patrol north of Baghdad, killing three officers and wounding four, police said.
The patrol had just pulled into a car park where they usually leave their vehicles while manning a checkpoint near a railway line, when the attack happened, police Lieutenant Ahmed Khalaf Ali said.
Patrol members returned fire, he said. There was no immediate word of casualties among the assailants.
Car bombings continue to be a
favoured tactic of Iraqi fighters
In other incidents, five civilians were wounded when a car bomb exploded in southern Baghdad, police said. The target of the explosion was not clear.
In western Baghdad, a civilian was killed and his wife was wounded when a car bomb struck at a US patrol, police said.
In Baquba, a car bomb killed one civilian and wounded three police officers. The policemen had arrived in the scene after assailants had killed a policeman during a patrol.
In central Hilla, 100km south of Baghdad, three traffic policemen and four civilians were wounded when a car bomb went off. Another car bomb exploded in northern Hilla, but no casualties were reported.
A policeman was wounded when four mortar rounds landed in and around Balad police office in Balad, 90km north of Baghdad, police said.
Elsewhere, three policemen were killed and four were wounded when armed men attacked their patrol in the oil refinery city of Baiji, 180km north of Baghdad, police said.
And in Tikrit, 175km north of Baghdad, a Sunni shrine was destroyed on Monday when armed men planted bombs inside it, police said.
A senior British general in Baghdad said in an interview published on Tuesday that most of Britain's 8000 troops in Iraq could be withdrawn by the middle of 2008. The UK Ministry of Defence, however, described that as one possible scenario.
The Daily Telegraph, which interviewed Lieutenant-General Nick Houghton in Baghdad on Monday, quoted him as saying the troops could largely be withdrawn in a four-phase process ending in the middle of 2008.
"Speculation on dates for handover and force levels is just that - speculation. General Houghton outlined one possible scenario among many," the Ministry of Defence said in a statement released on Tuesday.
The Christian Peacemaker Teams
men were abducted in November
"There is a fine line between staying too long and leaving too soon," the Telegraph quoted Houghton as saying.
"A military transition over two years has a reasonable chance of avoiding the pitfalls of overstaying our welcome but gives us the best opportunity of consolidating the Iraqi security forces."
The UK Ministry of Defence commented: "The general was commenting on recent speculation on the timing of handover. He made it clear that all of this was conditions-based and was outlining possible scenarios for handover, but the key point is that no decisions on timing or future force levels have been taken."