According to a recent report by Stanford and New York Universities’ law schools (Living Under Drones), the current US drone strike policy is counterproductive, has injured and killed civilians and undermines respect for international law. In june this year, Christof Heyns, the UN special rapporteur on extrajudicial killings, summary or arbitrary executions, told a conference in Geneva that the US policy of using drones to carry out targeted killings presents a major challenge to the system of international law that has endured since the Second World War. The US put out a statement in Geneva saying there was "unequivocal US commitment to conducting such operations with extraordinary care and in accordance with all applicable law, including the law of war".


A drone also known as unmanned aerial vehicles (UAVs), remotely piloted aircraft or unmanned aircraft system (UAS) is defined as a powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expandable or recoverable, and can carry a lethal or nonlethal payload. While there are dozens of different types of drones, the main categories are those that are used for reconnaissance and surveillance purposes and those that are armed with missiles and bombs.

The use of drones is on the rise. Drones are relatively inexpensive and because they have no pilot when one is shot down, the political price back home is minimal.  A US Congress report states that between 2004 and 2011, the number of countries that posses drones rose from 41 to 76, though just a small number of those nations possess armed drones. Currently only the US, Great Britain and Israel are known to have used armed UAVs. It is the weapon of choice for fighting terrorism. The first U.S. armed drone attack, which appears to be the first such strike ever, took place in mid-November 2001 and killed the military commander of Al Qaeda, Mohammed Atef, in Afghanistan. Since 2001 the number of drone attacks has dramatically increased. Although the drone strikes into Pakistan dominate the news now, they have also been employed in Iraq, Libya, Somalia and Yemen.


Most legal criticism focuses on the use of drones in other states’ territory and the civilian deaths caused by the drone attacks, so as governments are increasingly relying on drones, it bears examining when governments legally may resort to drone attacks. This blog explores briefly both the ius ad bellum and ius in bello implications of drone attacks.

Ius ad bellum

The ius ad bellum governs the resort to force by states. The United Nations Charter prohibits all uses of force with three exceptions:

  • States may use force with the Security Council’s authorization (Libya in 2011).
  • States may use force with the consent of a widely-recognized government on the territory of that consenting state. Although there is some evidence that the leadership in Pakistan tacitly consented to the drone attacks, Pakistan has not officially consented to the attacks and has often publicly protested the strikes.
  • States may use force in self-defense. Although the International Court of Justice (ICJ) in its jurisprudence has said several times that the armed attack must be attributable to a state for the exercise of self-defense, the Security Council and international organisations like the NATO and the OAS, seem to have extended the right to self-defense to terrorist forces, as in the case of the military operations in self-defense against Al-Qaeda in Afghanistan. When terrorists seek sanctuary in another state and that state fails to take appropriate action commentators disagree if a state that has been attacked by the terrorists may act militarily in self-defense in the other state.

The use of force, to be lawful, must fall under one of these three exceptions. But, in addition, ius ad bellum also requires that the action meets standards of “necessity” and “proportionality”. The principles of necessity and proportionality impose important conditions on the right to exercise force in self-defense.  Necessity requires that no viable alternative to the use of force exist before a state may resort to self-defense. Proportionality requires that a state acting defensively employs no more force than reasonably required to overcome a threat.

Ius in bello

Ius in bello, also known as international humanitarian law (IHL) , the law of armed conflict (loac) or law of war governs how force is used once an armed conflict is underway and how persons are protected during conflict. Ius in bello applies however only in the event of an armed conflict. Some commentators content that drone strikes in places like Yemen and Pakistan violate international law because there is currently no armed conflict occurring in these nations. So the question to be answered by the international community is if and when terrorism constitutes an armed conflict.

Traditionally the fundamental principles of the ius in bello are composed of a) military necessity b) distinction and c) proportionality, with many now adding to the list d) the principle of humanity.

The principle of military necessity holds that armed attacks in wartime be limited strictly to military objectives and offer a definite military advantage (Geneve Protocol I). The principle of distinction mandates that all parties to a conflict distinguish between those who are fighting and those who are not, and direct attacks only at those who are fighting. The principle of proportionality seeks to minimize incidental casualties during an armed conflict. Finally, the principle of humanity or unnecessary suffering aims to minimize suffering in an armed conflict. Weapons that cause unnecessary suffering are outlawed.

Although drones can’t be considered as unlawful weapons, the principles as outlined above need to be reviewed critically on a case-by-case basis before the decision is made to use an armed drone. Reports like “Living Under Drones” raise serious concerns about the compliance of particular strikes with the principles and although drones are said to be accurate, they still kill civilians. Critics of drone attacks allege that the number and frequency of civilian deaths are disproportionate to the military advantage they provide, the more so as civilian losses and drone attacks generate increased hostility among the civilian population and fuel terrorism.

Although ius in bello and ius ad bellum has not answered all the questions relating to the war on terror and drone warfare there are more than enough rules for governing drone warfare. It is up to policymakers at the international level to use these rules fairly and consistently.

Librarian's choice

A selection of relevant publications from the Peace Palace Library collection


Relevant PPL-keywords for further research

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