text: Conduct of Hostilities
  before carrying out an attack. In particular, the following practices are not prohibited: surprise attacks
  (paragraph 2-97); attacks on retreating forces (paragraph 2-98); harassing fires (paragraph 2-99); and attacks
  on specific individuals (paragraph 2-100).
  Surprise Attacks
  LOAC does not prohibit the use of surprise to conduct attacks, such as the use of surprise in ambushes,
  sniper attacks, air raids, and attacks by special operations forces carried out behind enemy lines. LOAC does
  not require that an enemy combatant be warned before being attacked. Rather, warning requirements only
  apply with respect to the civilian population and other certain protected units, vessels, and facilities, such as
  military medical facilities (see paragraphs 2-83 through 2-86).
  Attacks on Retreating Forces
  Enemy combatants remain liable to attack when retreating. Retreat is not the same as surrender.
  Retreating forces remain dangerous as the enemy force may recover to counterattack, consolidate a new
  defensive position, or assist the war effort in other ways. Retreat also may be a ruse. Retreating enemy
  combatants may have the same amount of force brought to bear upon them as an attacking military force,
  and a military commander is under no obligation to limit force directed against enemy combatants because
  they are, or appear to be, in retreat.
  Harassing Fires
  Although attacks to terrorize the civilian population are prohibited, harassing fires against enemy
  combatants are not prohibited. Harassing fires are delivered on enemy locations for the purpose of disturbing
  enemy forces’ rest, curtailing their movement, or lowering their morale.
  Attacks on Specific Individuals
  Military operations may be directed against specific enemy combatants. Often U.S. forces have
  conducted such operations (for example, the attacks against Osama bin Laden and Abu Musab Al Zarqawi).
  Siege
  It is lawful to besiege enemy forces, i.e., to encircle them with a view towards inducing their
  surrender by cutting them off from reinforcements, supplies, and communications with the outside world.
  The conduct of a siege or encirclement may require the imposition of measures of control to ensure that
  outsiders may not deliver supplies to the enemy. Thus, the right to conduct a siege or encirclement impliedly
  recognizes the authority of the military commander to exercise control, such as stopping, searching, and
  diverting traffic) over civilians and other persons in the immediate vicinity of military operations (DOD Law
  of War Manual, 5.19.1).
  A force besieging enemy forces may bar all communications and access between the besieged place
  and the outside. LOAC, however, requires belligerent States to make reasonable, good-faith efforts to
  conclude local agreements for the removal of wounded, sick, infirm and aged persons, children, and maternity
  cases from the besieged or encircled area and to permit the passage of ministers of all religions, medical
  personnel, and medical equipment to such areas (GC art. 17). In the past, it was permissible, but an extreme
  measure, to refuse to allow civilians to leave a besieged locality and to use force to drive any who attempted
  to flee back into the besieged locality. However, such actions are now prohibited because they are
  inconsistent with the duty to take feasible precautions for the protection of civilians (see DOD Law of War
  Manual, 5.19.4.1).
  Denial of Quarter Prohibited
  It is forbidden to declare that no quarter will be given (see HR art. 23(d)). This means that it is
  prohibited to order that legitimate offers of surrender will be refused or that detainees, such as unprivileged
  belligerents, will be summarily executed. Moreover, it also is prohibited to conduct hostilities on the basis
  that there shall be no survivors, or to threaten the adversary with the denial of quarter.