from HRW:
IV. LEGAL STANDARDS
In any armed conflict the right of the parties to choose the methods and means of warfare is not unlimited. On the contrary, those choices are strictly regulated by the customs and provisions of the law of armed conflict, referred to here as international humanitarian law (IHL). 102 IHL also regulates cases of total or partial military occupation, as in the case of the Palestinian territories. Against this background, certain episodes of violence that rise to the level of armed conflict are governed by general principles of the laws of war.
Some of the rules of IHL form part of international customary law, which are binding on all states and also on non-state actors-in this case, Palestinian armed groups.103
Many rules of IHL have been codified in international treaties, such as the Geneva Conventions and their additional protocols.
The Geneva Conventions have achieved widespread acceptance among states as authoritative standards of behavior for parties in situations of armed conflict, and have been ratified by more than 190 states.104 The 1977 Additional Protocols to the Geneva Conventions were negotiated at a diplomatic conference
where representatives from non-state armed groups campaigning for national self-determination were also present, including the Palestine Liberation Organization (PLO). Many of the provisions are recognized as customary international law.
Obligations of the Palestinian Authority and Armed Palestinian Groups
The rules and obligations of IHL are clearest when applied to conflict between sovereign states. The responsibilities of non-state actors may differ from those of sovereign states, but non-state actors, too, have clear responsibilities under IHL.
Many customary rules of IHL apply to all parties to a conflict, including non-state actors, provided that the confrontation is of an intensity that places it beyond the threshold of a mere disturbance.
Although it is not a sovereign state, the Palestinian Authority has explicit security and legal obligations set out in the Oslo Accords...
Crimes Against Humanity
The scale and systematic nature of the attacks on civilians detailed in this report meets the definition of a crime against humanity. Hamas and Islamic Jihad have claimed responsibility for suicide bombing attacks on civilians since 1994, and such attacks
clearly represent organizational policy at the highest levels. Since January 2002, the al-Aqsa Martyrs' Brigades and the PFLP have also claimed responsibility for organizing and carrying out such attacks.
The notion of "crimes against humanity" refers to acts that, by their scale or nature, outrage the conscience of humankind. Crimes against humanity were first codified in the charter of the Nuremberg Tribunal of 1945. Since then, the concept has been incorporated into a number of international treaties, including the Rome Statute of the International Criminal Court (ICC).
Although definitions of crimes against humanity differ slightly from treaty to treaty, all definitions provide that the deliberate, widespread, or systematic killing of civilians by an organization or government is a crime against humanity. Unlike war crimes, crimes against humanity may be committed in times of peace or in periods of unrest that do not rise to the level of an armed conflict.
The most recent definition of crimes against humanity is contained in the Rome Statute of the ICC, which entered into force on July 1, 2002. The statute defines crimes against humanity as the
"participation in and knowledge of a widespread or systematic attack against a civilian population," and
"the multiple commission of [such] acts...against any civilian population, pursuant to or in furtherance of a State or organizational policy to commit such attack." The statute's introduction defines "policy to commit such attack" to mean that the state or
organization actively promoted or encouraged such attacks against a civilian population. The elements of the "crime against humanity of murder" require that (1) "the perpetrator killed one or more persons," (2) "[t]he conduct was committed as
part of a widespread or systematic attack directed against a civilian population," and (3) "[t]he perpetrator knew that the conduct was part of, or intended the conduct to be part of, a widespread or systematic attack against a civilian population."
Those who commit crimes against humanity, like war crimes, are held individually criminally responsible for their actions. Crimes against humanity give rise to universal jurisdiction, they do not admit the defense of following superior orders, and they do not benefit from statutes of limitation.
International jurisprudence and standard setting of the last ten years have consolidated the view that those responsible for crimes against humanity and other serious violations of human rights should not be granted amnesty. As in the case of war crimes,
all states are responsible for bringing those who commit crimes against humanity to justice.
The pattern of suicide bombing attacks against Israel civilians that emerged in 2001 and intensified during 2002 clearly meets the criteria of a crime against humanity.
http://www.hrw.org/reports/2002/isrl....htm#TopOfPage
you can't get any clearer than that, can you?