To be legally justified, a reprisal can only be directed against the party carrying out the original violation, can only be carried out as a last resort, after having given formal notice of the planned reprisal, must be proportionate to the original violation, must have the aim of persuading the original violator to comply with the legally accepted behavior in future, and must not continue after the illegal behavior ends.
Circumstances usually dictate that reprisals can only be taken against people guilty of the original violation. However, there is always a probability that the reprisals will themselves be viewed as hostile acts, risking a vicious circle of violations by both sides.
All four Geneva Conventions prohibit reprisals against, respectively, battlefield casualties, shipwreck survivors, prisoners of war and civilians, as well as certain buildings and property. An additional 1977 protocol extends this to cover historic monuments, works of art and places of worship.