Article 51 of the First Protocol Additional to the 1949 Geneva Conventions is the relevant law.
The approach of international law applied to armed conflicts is that enemy civilians are protected from attacks by the military. However, that protection does not extend to civilians who take part in hostilities. Harming such civilians, even if the result is death, is permitted provided there is no other option that would be less harmful, and on condition that innocent civilians nearby are not harmed, at least not harmed disproportionately. According to this provision, a civilian who takes violent action against the enemy does not lose his civilian status, but loses the protected status of a civilian during the time that he was involved in the violent action.
In a ruling by the Israeli High Court of Justice, in order for a targeted killing to be considered legal, the state must fulfill four conditions to the best of its ability...
It sounds like the Israeli High court of Justice has done their best to assure that targeted killings are only performed as a last resort.
1) It must have strong evidence that the potential target meets the conditions for having lost his protected status.
This provision disturbs me, as it would seem that the government decides whether the evidence is strong or not. Of course, the US does the same. It led to the Iraq war.
2) An independent and thorough investigation must be conducted immediately after the operation to determine whether it was justified. In appropriate cases, the state should compensate innocent civilians for harm done.
It would seem to me that the time for the independent and thorough investigation would be before the target is killed. Otherwise, there is no effective remedy for the inappropriately targeted victim.
Who provides this "independent and thorough investigation?" International human rights groups? Israeli judiciary? It has the potential to be a rubber stamp.
3) If less drastic measures can be used to stop the potential target posing a security a threat, such as arrest, the state must use them, unless this alternative poses too great a risk to the lives of the soldiers.
Again, reasonable on its face. The question, of course, it what a "reasonable" level of risk to soldiers is. Israel killed hundreds of Palestinian civilians in January to avoid the risk of the loss of soldiers. It would seem that they are willing to sacrifice many Palestinian lives to avoid the risk to their troops.
Or perhaps not. They may simply have come to the decision that a commando raid would both be more risky and less likely to succeed than a missile from a drone.
4) The state must assess in advance whether the collateral damage to innocent civilians involved in a targeted killing is expected to be greater than the advantage gained by the operation. If it is, the state must not carry out the operation.
Another slippery definition that is hard to challenge. Is a key Hamas terrorist worth 5 civilians, 50 civilians, 500 civilians, or more? Do children count the same as adults? It's a pretty flexible standard.
If the state performs all four duties and finds that the proposed actions meet the conditions set forth in the law, the targeted assassination will be legal, concluded the Court.
The guidelines are reasonable, but as with any situation such as this the devil is in the details. Who makes up the independent commission, and by what standards do they judge the evidence as "strong" and whether the advantage gained was worth the collateral damage? And as important, are these results released for public scrutiny, or do we just need to take the Israeli government's word for it that a particular operation was justified?
So as not to be seen as picking on Israel, these procedures may well be more rigorous than those in the US.