The recent shootings of Michael Brown, Tamir Rice, and John Crawford III by police officers in the US, has sparked debate about how police engage suspects, when they are allowed to use force, and how much force they can use.
Reuters photographer Marko Djurica put together a gallery of images of police and tactical units from around the world, detailing their equipment and rules of engagement.
Ferguson, Missouri.
Left: A police officer raises his weapon at a car speeding in his general direction. Right: Police use smoke and tear gas to disperse protestors as they became unruly, August 18, 2014.
In the US, police are allowed to use deadly force to protect their life or the life of another innocent party, or to prevent someone suspected of committing a serious violent felony from escaping.
Left: Police follow protesters during a march. Right: An LAPD officer in full riot gear.
New York City.
Serbia.
Left: Special Anti-Terrorist Unit. Right: Serbian gendarmerie officers.
In Serbia, police may use measures ranging from batons to special vehicles, water cannon and tear gas on groups of people who have gathered illegally and are behaving in a way that is violent or could cause violence, but they may use firearms only when life is endangered.
Mexico.
In Mexico, "when violent action by a crowd cannot be deterred, a scale of force will be applied progressively consisting of 1. verbal persuasion or deterrence 2. reduced physical movements 3. use of non-lethal incapacitating weapons, and 4. use of firearms or lethal force".
Malaysia.
In Malaysia, the FRU are only permitted to use firearms in cases where the protesters are using firearms. Firearms have not been used in the 59 years since the FRU was formed.
Belgium.
In Belgium, police are legally entitled to use proportionate force, after a warning, where there is no other means to achieve a legitimate objective. Police may use firearms in self-defense, to confront armed perpetrators, or in defense of persons or key facilities, but never for crowd control.
United Nations, Geneva, Switzerland.
U.N. police in Geneva follow the local cantonal police rules, which say that "the use of weapons, proportionate to the circumstances, is authorised as a last resort" but should "avoid serious injury whenever possible", and that "the use of a firearm is preceded by a warning if circumstances permit".
The United Nations Office in Geneva is considered ex-territorial and is not under the jurisdiction of the host country Switzerland.
Philippines.
Left: Philippine National Police bomb squad members with a bomb scanner and bomb suit at a police station in Manila.
Right: A member of Philippine National Police with a patrol segway, in front of a police station in Manila.
In the Philippines, the use of extreme force against a suspect is allowed only if the police officer's life or that of the victim (or the suspect) is in imminent danger.
Venezuela.
In Venezuela, no firearms are to be carried or used for control of peaceful demonstrations. When there is a threat to order, and other methods of conflict resolution have failed, police are instructed to warn crowds or demonstrators that there will be a "progressive, differentiated use of force".
Measures are to be taken to avoid harming children, the elderly and other vulnerable groups, and no force is to be used on those who avoid violence or are withdrawing from the scene.
Austria.
In Austria, the use of lethal force is permitted to tackle rioting or to detain a dangerous suspect, but only when less dangerous methods "appear inappropriate or have proved to be ineffective", and with the aim of avoiding serious injury where possible. The use must be proportionate, and be preceded by a warning.
Bosnia.
In Bosnia, police are permitted to use force ranging from batons to chemical irritants, water cannon, "binding agents, special firearms and explosive devices", following a warning, but only when other methods of control have proved ineffective, and not against the young, old or disabled unless these use firearms.
The method must be "proportional to the resistance or violence coming from the person on whom the force is used".
India.
In India, the Rapid Action Force (RAF) are called on for violent disorder that the police are unable to contain. They require an on-the-spot magistrate's consent and must issue a warning before each escalation of the use of force, from verbal warning to water cannon and tear gas, then to rubber bullets or baton rounds, and then to firearms.
Afghanistan.
Left: Afghan policemen in Kabul (R-L) Shir Agha, 24, Shkib, 24, Qayam, 22, Farid Ahmad, 26, and Sobhan Ullah, 22. Right: Afghan policeman Zabiullah, 24.
In Afghanistan, "the police can use weapons or explosives against a group of people only if they it has ... disturbed security by means of arms, and if the use of other means of force ... has proved ineffective". Afghan police are required to give no fewer than six warnings - three verbal and three warning shots - before using force in this situation.
Italy.
In Italy, police and the paramilitary Carabinieri follow the same guidelines, which say that the use of weapons is allowed only in the line of duty, when it is an "unavoidable necessity to overcome resistance, stop violence, or prevent a [serious] crime", and that the response must be proportionate to the situation.
Great Britain.
In Britain, "lethal or potentially lethal force should only be used when absolutely necessary in self-defense, or in the defense of others against the threat of death or serious injury."
According to What is Policing? by P.A.J. Waddington and Martin Wright, the decision not to arm Metropolitan Police and equip them with non-military uniforms (they wore blue, the army wore red) was 'a consciously political decision on the part of Sir Robert Peel to distance the police from the military. The police were disarmed as a conscious policy of winning political legitimacy.'
Despite popular belief to the contrary, British police have always had access to arms, and since 1984, specially trained officers have been issued with MP5 sub-machine guns (pictured above).
According to the book Shooting to Kill: Policing, Firearms and Armed Response by Peter Squires and Peter Kennison, "in the view of the government and large sections of the tabloid press the resort to machine guns was 'unfortunate, but necessary'."