Rumors and speculations:

http://www.peace.ca/geneticwarfare.htm
http://abbc.com/islam/english/toread/bomb.htm
http://msanews.mynet.net/MSANEWS/199811/19981119.41....

... and on the other hand, what seems to be an unbiased, scientific opinion:

Whether such weapons are possible is debatable, at least with
our current knowledge. Race is as much a cultural
phenomenon as a biological one – the human genome
shows that there is more genetic variation within racial groups
than between them. So the chances of finding a trait universal
within an ethnic group yet limited to it, and which could be
used to target a bioweapon, seem remote.

But, comments bioethicist Jonathan Mereno of the University
of Virginia, Charlottesville, "we can predict that attempts will
be made to develop such weapons" – probably involving
experiments on human subjects.

from http://www.nature.com/nsu/010222/010222-17.html