Washington wants its soldiers to be immune from Afghan courts if they remain after 2014. Kabul isn't sure. Here are five things to know about what makes immunity for foreign soldiers so complicated.
How has immunity become a sticking point for keeping U.S. soldiers in Afghanistan?
Both Kabul and Washington want some U.S. soldiers to remain in Afghanistan after multinational forces leave by the end of next year. But they cannot agree upon the terms of a Status of Forces Agreement (SOFA) detailing how much immunity U.S. soldiers will have from Afghan courts.
Afghan President Hamid Karzai and U.S. Secretary of State John Kerry acknowledged the sticking point in Kabul on October 2, when they announced only partial success in writing a new security pact.
Karzai said he will ask a "loya jirga" assembly of tribal leaders next month to decide whether U.S. soldiers should have immunity. Kerry said that without immunity, U.S. soldiers will not be able to stay.
Why do countries demand immunity for their soldiers?
Governments sending troops abroad have historically demanded a special legal status for them. One reason is they fear the courts of the host country may grant weaker protections to people accused of crimes than do their own justice systems.
This is particularly true of Western states whose legal systems provide strong rights to the accused. That includes protection against forced confessions, the right to representation by a lawyer, and the right to challenge detentions based on insufficient evidence.
Additionally, governments worry that court systems in host countries can be subject to negative popular pressure, particularly if there is resentment of foreign soldiers' presence.
But it's important to understand that governments are requesting immunity, not impunity, for their soldiers.
"In these agreements, it is not only that the country sending troops demands -- and obtains, usually -- protection and immunity for its forces. There is also a very strong obligation on the foreign forces deployed to strictly abide by the laws of the host nation," says Marc Finaud, an expert in international security at the Switzerland-based Geneva Center for Security Policy.
"And if there are breaches or severe violations of these laws and regulations by members of the foreign troops, obviously they have to be prosecuted and sentenced [in their home countries] for those violations."
That means governments sending soldiers abroad expect them to respect the laws of the host country as well as to obey the laws of their homeland. They are not giving their soldiers freedom to break laws.
Why are host countries uncomfortable with granting immunity?
Host countries often see granting immunity to foreign soldiers as a diminishment of their national sovereignty. Feelings are particularly high in times of war, when foreign combat troops conduct military operations that may endanger civilians.
But even in peacetime, there are problems. Local people may be outraged when individual soldiers commit crimes and then are tried far away under unfamiliar systems of justice.
Michael Codner, a researcher in military science at the London-based Royal United Services Institute, says that is especially true for serious crimes. Murder might be punishable by death in one country, such as Afghanistan, but not another, like Britain.
"It will obviously be an uncomfortable situation if the legal systems are very different. For instance, if Britain has its forces in a country and murder is committed and that country has the death penalty, then the British soldier would be [expected to be] submitted to the death penalty, which is against British law," Codner explains.
Governments sometimes address these concerns by helping people from the host country attend trials. In August, a group of Afghan victims and witnesses were flown to the United States for the sentencing hearing of Robert Bales, who murdered 16 people last year in Kandahar Province. The military court did not hand down a death sentence, as many Afghans had called for, but life imprisonment instead.
How much do immunity agreements between countries vary?
There is no fixed standard. In some, states retain exclusive jurisdiction over their soldiers. In others, they share jurisdiction with the host country. The choice often depends upon the closeness of two countries' ties.
"Countries that are already related to each other through alliances may have basic agreements existing before the specific SOFA agreements are concluded. And it may simplify these agreements, because they already know each other's legal systems and they may be more similar," says Nils Melzer, an international and security law expert at Geneva Center for Security Policy.
"It will be easier for them to share jurisdiction than it will be when you have two very different legal systems, as may be the case between the United States and Afghanistan."
Sometimes, public reaction in host countries to particularly heinous crimes can affect how immunity agreements are applied. One example is the 1995 rape of a 12-year-old girl in Japan by three U.S. servicemen. Afterward, Washington agreed to give favorable consideration to future Japanese requests to immediately hand over suspects in rape and murder cases to local police for questioning. Previously, Washington had refused to hand over suspects until they were formally charged.
Can disagreements over immunity make it impossible for foreign troops to stay?
How seriously countries regard immunity can be seen in the inability of the United States and Iraq to reach an agreement before the scheduled withdrawal of U.S. soldiers in 2011.
The failure scuttled plans to leave a U.S. military-training presence to help Iraqi forces fight a counterinsurgency war against militant groups, a war which continues today.