An attack shall be cancelled or suspended if it becomes apparent that the objective is not a military one or is subject to special protection or that the attack may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated. 

In practice, it is extremely difficult to stop an attack. The obligation does not extend below the levels of commanders who have the authority and practical possibility to do so; say a commander of a battalion group. The obligation is in any event subject to the knowledge principle … which means that its application will be rare.