The latest conflict in the Middle East has brought a shift in how international law views states which are linked to terrorism, writes Tom Cooney.
International law bears on Israel's most recent responses to Islamic jihadist terrorism. There is first Israel's military response to Hizbullah attacks from Lebanon.
The G8 statement on the Hizbullah's terrorist attack on Israel is significant because it recognises Israel's right under international law to use military force to defend itself. This tells us that international law has moved on in two ways.
First, contrary to the International Court of Justice's stance, the international community accepts that Israel has a right of self-defence under article 51 of the United Nations Charter, even though Hizbullah is not a state.
Second, Israel may hold Lebanon directly responsible for the attack
Since 9/11, the threat of international terrorism has forced states to recognise that a state that culpably fails to prevent terrorist attacks or facilitates terrorist groups is directly responsible for the attacks. The underlying principle is that states must counter international terrorism.
Lebanon hosts Hizbullah - its terrorist leaders, operatives, trainers and planners, even though it knows what it does. Hizbullah shares government. UN security council resolution 1559 obliged the Lebanese government to disarm Hizbullah.
Instead, the government has facilitated Hizbullah, allowing Syria and Iran to arm, train and supply it.
Hizbullah's attacks on Israel resulted, therefore, from Lebanon's failure to counter international terrorism. Lebanon is like a police officer who harbours a killer, helps him to get his gun and then assists him to target his victim.
Since Lebanon materially contributes to Hizbullah's terrorist activity, it is responsible for the attack on Israel.
Iran and Syria must shoulder direct responsibility, too. Israel's armed response must target combatants and be proportionate to the terrorist threat.
Next is the military operation to rescue its kidnapped soldiers. The terrorist operations to seize the soldiers were an attack on the Israeli government and violated international law. On even the narrowest interpretation of international law, an Israeli rescue mission is an act of self-defence under article 51 of the UN Charter.
Any rescue operation must be proportionate. The magnitude of the in-out military rescue operation must be designed to effect a rescue and the action must be necessary to save the soldiers.
Here the threat of death to the soldiers is imminent. Neither the Palestinian Authority (PA) nor the Lebanese government has tried to rescue them so diplomatic means have failed. The Israeli response is immediate thus preserving a nexus between the terrorist seizure of the soldier and the rescue mission.
There is, finally, Israel's decision to increase interceptive strikes by the IDF against terrorists firing rockets into Israel. Israel has a moral and legal right to defend itself against trans-boundary terrorism.
The objective of terrorist attacks is to murder innocent Israelis. Their scale and effects have been significant. Because neither the PA nor the Lebanese government has tried to prevent terrorists from using their land as a springboard for those attacks, Israel is entitled to engage in self-help.
Some say that Israel may only make a law-enforcement response. Israel must try first to arrest the terrorists. Interceptive killing is lawful only if the lethal force is absolutely necessary to defend Israelis from imminent acts of unlawful violence.
The terrorists are civilians so they may be targeted only when they are carrying out their terrorist acts. When they complete their terrorist acts, they become civilians once again.
This analysis is feeble. To enforce the law, Israel must be able to arrest the terrorists. Terrorists in Gaza, for example, are not within Israel's grasp. Trying to arrest them would cause many civilian casualties.
Secondly, policing targets acts of individual wrongdoing, but Palestinian terrorists engage in a systematic pattern of intense terrorist violence to serve ideological ends against Israel. They are organised combatants, not civilians.
The principle of distinction says that civilians have a legal shield against direct military attacks so the IDF must refrain from harming civilians insofar as possible. Terrorists however can't fight Israel and remain civilians.
In armed conflict, you are either a civilian or a combatant. Civilians who take part in hostilities lose their legal protection and expose themselves to attack as combatants.
Palestinian and Hizbullah terrorists though are not lawful combatants. They often do not wear a fixed distinctive insignia on their persons or vehicles throughout their operations. Combatants must be distinguishable from civilians. They often do not carry their arms openly. Their war crimes - including directly attacking civilians - turn them into unlawful combatants.
For these violations, Israel may, if it captures the terrorists, punish them. It can deny them the benefits of prisoner-of-war status. It can detain them or try them for their crimes of violence before its courts. The law of armed conflict doesn't give them immunity (as it does a lawful combatant) from prosecution for killing their enemy.
Crucially, so long as they involve themselves in hostilities, Israel may target them with interceptive strikes, but the strikes must be a necessary and proportionate response intended to defend Israelis against further attacks.
True, interceptive strikes endanger civilians and, although the terrorists hide among Palestinian civilians, this doesn't strip those civilians of their protected status. While the terrorists are legitimate military targets, the civilians are not. So civilians have a right not to be arbitrarily deprived of their lives.
This complication though doesn't mean that Israel must stop its attacks. Depending on the context, such attacks are permissible.
Firstly, the terrorists and their planners are a military objective and a lawful target. Secondly, attacking them is a military necessity to prevent them from killing Israelis. Thirdly, the means of attack - with precision weapons - is permissible and not indiscriminate.
The principle of proportionality, however, requires that military targets must be attacked in a way that minimises civilian casualties and damage, so incidental damage to civilians must not exceed what is necessary to achieve a legitimate military objective.
Commanders must assess the likely casualties, both military and civilian, and weigh that against the concrete and direct military advantage they expect to gain. The International Criminal Tribunal for Yugoslavia in the Martic case and in the Kupreskic case said that this requirement was a general principle of international law.
For the G8 leaders, fighting international terrorism sometimes demands a military response. The insight is that the law-enforcement model is inadequate when an ideologically driven non-state aggressor (like Hizbullah or Hamas) has the ability to destroy in ways that we used to assume that only states with armies could deploy.
It is also that any state which hosts or facilitates international terrorists bears responsibility for their attacks. That's a significant change.
Tom Cooney teaches law at University College Dublin's law school