Brown made the plea days after the captors released a video of one of the men and said they would kill them all unless Britain withdrew all its troops from the country.
"The taking of hostages is completely unjustified, wholly unacceptable and we are making it clear they will not change our policy in any way," Brown said.
"We will do everything in our power to secure our objective, which is the immediate release of the hostages."
The four security guards and one computer expert were taken prisoner in May by abductors dressed as Iraqi police in a finance ministry building in Baghdad.
Güncelleme Tarihi: 09 Aralık 2007, 18:45