International humanitarian law (IHL) is the body of international law applicable when armed violence reaches the level of armed conflict, whether international or non-international. The best known IHL treaties are the four Geneva Conventions of 1949 and their two Additional Protocols of 1977, but there are a range of other IHL treaties aimed at reducing human suffering in times of war, such as the 1997 Ottawa Convention on landmines.

IHL - sometimes also called the Law of Armed Conflict or the Law of War - does not provide a definition of terrorism, but prohibits most acts committed in armed conflict that would commonly be considered "terrorist" if they were committed in peacetime.

It is a basic principle of IHL that persons fighting in armed conflict must, at all times, distinguish between civilians and combatants and between civilian objects and military objectives. The "principle of distinction", as this rule is known, is the cornerstone of IHL. Derived from it are many specific IHL rules aimed at protecting civilians, such as the prohibition of deliberate or direct attacks against civilians and civilian objects, the prohibition of indiscriminate attacks or the use of "human shields". IHL also prohibits hostage taking.

In situations of armed conflict, there is no legal significance in describing deliberate acts of violence against civilians or civilian objects as "terrorist" because such acts would already constitute war crimes. Under the principle of universal jurisdiction, war crimes suspects may be criminally prosecuted not only by the state in which the crime occurred, but by all states.

See the Treaty database, containing about 100 IHL treaties, the four Geneva Conventions and their Additional Protocols and an up-to-date list of signatures and ratifications

Yes, IHL specifically mentions and in fact prohibits "measures of terrorism" and "acts of terrorism".

The Fourth Geneva Convention (Article 33) states that "Collective penalties and likewise all measures of intimidation or of terrorism are prohibited", while Additional Protocol II (Article 4) prohibits "acts of terrorism" against persons not or no longer taking part in hostilities. The main aim is to emphasise that neither individuals, nor the civilian population may be subject to collective punishments, which, among other things, obviously induce a state of terror.

Both Additional Protocols to the Geneva Conventions also prohibit acts aimed at spreading terror among the civilian population. "The civilian population as such, as well as individual civilians, shall not be the object of attack. Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited" (AP I, Article 51(2) and AP II, Article 13(2)).

These provisions are a key element of IHL rules governing the conduct of hostilities i.e. the way military operations are carried out. They prohibit acts of violence during armed conflict that do not provide a definite military advantage. It is important to bear in mind that even a lawful attack on military targets can spread fear among civilians. However, these provisions outlaw attacks that specifically aim to terrorise civilians, for example campaigns of shelling or sniping of civilians in urban areas.

As already mentioned IHL is only applicable in armed conflict. A central element of the notion of armed conflict is the existence of "parties" to the conflict. The parties to an international armed conflict are two or more states (or states and national liberation movements), whereas in non-international armed conflict the parties may be either states and armed groups – for example, rebel forces- or just armed groups. In either case, a party to an armed conflict has a military-like formation with a certain level of organization and command structure and, therefore, the ability to respect and ensure respect for IHL.

The rules of IHL apply equally to all parties to an armed conflict. It does not matter whether the party concerned is the aggressor or is acting in self-defence. Also, it does not matter if the party in question is a state or a rebel group. Accordingly, each party to an armed conflict may attack military objectives but is prohibited from direct attacks against civilians.

The equality of rights and obligations under IHL enables all parties to a conflict to know the rules within which they are allowed to operate and to rely on similar conduct by the other side. It is the existence of at least two parties to an armed conflict and the basic equality among them under IHL, as well as the intensity of violence involved and the means used, which distinguishes warfare from law enforcement.

Specific aspects of the so-called "war on terrorism" launched after the attacks against the United States on 11 September 2001 amount to an armed conflict as defined under IHL. The war waged by the US-led coalition in Afghanistan that started in October 2001 is an example. The 1949 Geneva Conventions and the rules of customary international law were fully applicable to that international armed conflict, which involved the US-led coalition, on the one side, and Afghanistan, on the other side.

However, much of the ongoing violence taking place in other parts of the world that is usually described as "terrorist" is perpetrated by loosely organized groups (networks), or individuals that, at best, share a common ideology. On the basis of currently available factual evidence it is doubtful whether these groups and networks can be characterised as a "party" to a conflict within the meaning of IHL.

Even if IHL does not apply to such acts they are still subject to law. Irrespective of the motives of their perpetrators, terrorist acts committed outside of armed conflict should be addressed by means of domestic or international law enforcement, but not by application of the laws of war.

Most of the measures taken by states to prevent or suppress terrorist acts do not amount to armed conflict. Measures such as intelligence gathering, police and judicial cooperation, extradition, criminal sanctions, financial investigations, the freezing of assets or diplomatic and economic pressure on states accused of aiding suspected terrorists are not commonly considered acts of war.

"Terrorism" is a phenomenon. Both practically and legally, war cannot be waged against a phenomenon, but only against an identifiable party to an armed conflict. For these reasons, it would be more appropriate to speak of a multifaceted "fight against terrorism" rather than a "war on terrorism".

States have the obligation and right to defend their citizens against terrorist attacks. This may include the arrest and detention of persons suspected of terrorist crimes. However, this must always be done according to a clearly defined national and/or international legal framework.

Persons detained in relation to an international armed conflict involving two or more states as part of the fight against terrorism – the case with Afghanistan until the establishment of the new government in June 2002 - are protected by IHL applicable to international armed conflicts.

Captured combatants must be granted prisoner of war status (POW) and may be held until the end of active hostilities in that international armed conflict. POWs cannot be tried for mere participation in hostilities, but may be tried for any war crimes they may have committed. In this case they may be held until any sentence imposed has been served. If the POW status of a prisoner is in doubt the Third Geneva Convention stipulates that a competent tribunal should be established to rule on the issue.

Civilians detained for security reasons must be accorded the protections provided for in the Fourth Geneva Convention. Combatants who do not fulfil the requisite criteria for POW status (who, for example, do not carry arms openly) or civilians who have taken a direct part in hostilities in an international armed conflict (so-called "unprivileged" or "unlawful" belligerents) are protected by the Fourth Geneva Convention provided they are enemy nationals.

Contrary to POWs such persons may, however, be tried under the domestic law of the detaining state for taking up arms, as well as for any criminal acts they may have committed. They may be imprisoned until any sentence imposed has been served.

Read the full text of the Fourth Geneva Convention

Persons detained in relation to a non-international armed conflict waged as part of the fight against terrorism – as is the case with Afghanistan since June 2002 - are protected by Article 3 common to the Geneva Conventions and the relevant rules of customary international humanitarian law. The rules of international human rights and domestic law also apply to them. If tried for any crimes they may have committed they are entitled to the fair trial guarantees of international humanitarian and human rights law.

Read more about the protection of victims of non-international armed conflicts
All persons detained outside of an armed conflict in the fight against terrorism are protected by the domestic law of the detaining state and by international human rights law. If tried for any crimes they may have committed they are protected by the fair trial guarantees of these bodies of law.

What is important to know is that no person captured in the fight against terrorism can be considered outside the law. There is no such thing as a "black hole" in terms of legal protection.

Under the Geneva Conventions, the ICRC must be granted access to persons detained in an international armed conflict, whether they are POWs or persons protected by the Fourth Geneva Convention.

It is in this context that the ICRC has been visiting a number of persons detained, for example, as a result of the international armed conflict in Afghanistan, both in Afghanistan and at the US naval base in Guantanamo Bay, Cuba. The ICRC has repeatedly called for a determination of the precise legal status of each individual held at Guantanamo Bay, as well as for a determination of the legal framework applicable to all persons held in the fight against terrorism by the US authorities.

If the fight against terrorism takes the form of a non-international armed conflict, the ICRC can offer its humanitarian services to the parties to the conflict and gain access to persons detained with the agreement of the authorities involved.

Outside of armed conflict situations, the ICRC has a right of humanitarian initiative under the Statutes of the International Red Cross and Red Crescent Movement. Thus, many persons regularly visited by the ICRC have been detained for security reasons in peacetime.
Some of the existing international conventions on terrorism include specific provisions providing that states may allow ICRC access to persons detained on suspicion of terrorist activities.

These provisions, as well as the ones included in IHL treaties and in the Statutes of the International Red Cross and Red Crescent Movement are in recognition of the unique role played by the ICRC, based on its principles of neutrality and impartiality.