In a new video shown by Aljazeera on Saturday and dated 21 January, the four hostages were shown standing against a wall in an unknown location.
The four - two Canadians, one Briton and one American - appeared to be speaking to the camera but their voices could not be heard.
A statement received along with the tape and read on air said the kidnappers were giving a "last chance" for US and Iraqi authorities to "release all Iraqi prisoners in return of freeing the hostages otherwise their fate will be death".
Briton Norman Kember, American Tom Fox and Canadians James Loney and Harmeet Sooden were kidnapped on 26 November in Baghdad, where they were working with a Christian peace organization.
Swords of Truth
They are being held by the previously unknown Swords of Truth.
On Monday the wife of the 74-year-old British hostage appealed for the release of her ailing husband in a televised message.
The Swords of Truth earlier issued a video of the four men and accused them of spying for US-led forces.
It threatened to kill them unless prisoners in Iraqi jails were freed.
Muslim scholars and activists from around the world, including leaders of the Hamas and Hizb Allah groups, have appealed for the release of the aid workers.
Many have been freed, but about 50 have been killed.