Ruth Lapidoth, Professor Emeritus of International Law at the Hebrew University of Jerusalem
* The relations between Israel and Hamas are in the nature of armed conflict. Nowadays no formal declaration of war is needed. Hence the rules of the laws of armed conflict apply. This means that Israel may control shipping headed for Gaza – even when the vessels are still on the high seas.
* The rules of naval warfare have not been fully codified in a treaty and are in the nature of binding customary rules. They can be found in the relevant manuals of Western armies (in particular the U.S. and Britain) and in the San Remo Manual prepared by a group of experts.
* In order to be legal, a blockade has to be declared and announced, effective, non-discriminatory, and has to permit the passage of humanitarian assistance to the civilian population. In addition, the San Remo Manual of 1994 includes two conditions: first, the state which applies the blockade may decide where and when and through which port the assistance should reach the coast. In addition, the state may require that a neutral organization on the coast should verify who is the recipient of the assistance. In Gaza, for instance, does it reach the civilians or Hamas?
* A ship that clearly intends to breach the blockade may be stopped already when it is still on the high seas. Stopping the flotilla heading for Gaza in international waters 100 kilometers from Israel was not illegal; in time of armed conflict, ships intending to breach the blockade may be searched even on the high seas.
* Israel is within its rights and is in full compliance with international law because it has fulfilled all of the above-mentioned conditions for a lawful blockade. E.g., in January 2009 Israel notified the relevant authorities of its intention to establish a blockade of the Gaza coast.