Cluster bombs are controversial weapons consisting of a canister which breaks apart to release a large number of small bombs. A range of so-called bomblets can be employed to attack different targets such as armoured vehicles or people - or to start fires.

They can cover a large area but do not have precision guidance. Dropped from medium to high altitudes, they can wander off target.

There is a significant "dud rate" of about 5%. In other words, many do not explode but, rather like landmines, litter the ground with the potential to explode years later. There are said to be thousands in Kosovo.