The medical charity Medecins Sans Frontieres (MSF) has accused U.S. forces of committing a "war crime" after the bombing of its hospital in the northern Afghan city of Kunduz on Saturday.
The U.S. military has taken responsibility for the airstrike, which killed 22 people, calling it a mistake and vowing to bring the perpetrators to account.
But MSF wants an independent investigation into the bombing. Here are five facts on war crimes, International Humanitarian Law and how it works.
WHAT IS A WAR CRIME?
War crimes are grave breaches of International Humanitarian Law (IHL) and are applicable to armed conflict when committed as part of a plan or policy, or on a large scale.
This includes murder, mutilation, cruel treatment and torture, intentionally directing attacks against the civilian population, sexual violence, taking hostages and recruiting children as soldiers.
WHAT IS INTERNATIONAL HUMANITARIAN LAW (IHL)?
IHL, often called the law of war, is a set of rules that try, for humanitarian reasons, to limit the effects of armed conflict.
A major part of IHL is contained in the four Geneva Conventions of 1949 that have been adopted by every nation in the world. These have been expanded and are supplemented by two further protocols, which some nations have not signed, among them the United States and Afghanistan.
The Conventions provide specific rules to safeguard combatants, or members of the armed forces, who are wounded, sick or shipwrecked, prisoners of war, and civilians.
WHO CAN INVESTIGATE A WAR CRIME?
IHL requires countries to seek out and punish any person who has committed a grave breach, irrespective of their nationality or the place where the offence was committed.
Ideally, the country where the alleged war crime occurred can probe the case, but other options are available, such as the U.N. Human Rights Council or the International Criminal Court (ICC) in The Hague.
The International Humanitarian Fact-Finding Commission, established under one of the Geneva Convention protocols, can investigate violations, such as attacks on hospitals which are protected in conflict zones. This body has never been used and neither the United States nor Afghanistan are signatories to the protocol establishing it.
Prosecutions can be brought only by national courts of different states or by the ICC, provided states involved are signatories to the Rome Statute which established the ICC.
HOW SUCCESSFUL HAS THE ICC BEEN IN SECURING CONVICTIONS FOR WAR CRIMES?
Since the ICC was established 13 years ago, it has obtained only two convictions out of the 23 cases in nine countries which have been brought before it.
In 2012, Thomas Lubanga, a militia leader in the Democratic Republic of Congo, was convicted of war crimes relating to the use of children in that country's conflict and sentenced to 14 years' jail.
In 2014, another Congolese warlord, Germaine Katanga, was sentenced to 12 years in jail for war crimes relating to murder, attacking a civilian population, destruction of property and pillaging.
WHY DOES MSF WANT TO USE THE IHFCC AND NOT THE ICC?
The MSF says the IHFCC is the best option for an independent investigation because it is the only body set up specifically for international humanitarian law violations.
"The facts and circumstances of this attack must be investigated independently and impartially, particularly given the discrepancies in the U.S. and Afghan accounts of what happened in the days following the attack," an MSF spokesman said.
"We cannot rely on only internal military investigations which would be wholly insufficient."
MSF says the first step is to establish the facts, which is the role of the IHFCC investigation. Once the facts are clear, it will be up to the United States and/or Afghanistan to prosecute those responsible.
The ICC can prosecute only if the state concerned does not, cannot or is unwilling to do so.