Here is an article by Leslie H. Gelb, a former New York Times columnist and president emeritus of the Council on Foreign Relations, from the Daily Beast, June 2:
Israel had every right under international law to stop and board ships bound for the Gaza war zone late Sunday. Only knee-jerk left-wingers and the usual legion of poseurs around the world would dispute this. And it is pretty clear that this "humanitarian" flotilla headed for Gaza aimed to provoke a confrontation with Israel. Various representatives of the Free Gaza Movement, one of the main organizers of this deadly extravaganza, have let it slip throughout Monday that their intention was every bit as much "to break" Israel's blockade of Gaza as to deliver the relief goods.
The Israeli commandos who stormed the ship, where fighting erupted, badly mishandled the situation. But theirs was a mistake in pursuit of a legal goal, not a war crime. And as for calls for international investigations, they represent the usual hypocritical nonsense that will go nowhere. Except for those who routinely fool themselves about the judiciousness and effectiveness of action by the United Nations or the European Union, everyone understands their "investigations" will amount to nothing. Only the United States might do something useful—if the White House would only seize quickly the practical solution staring it in the face.
Regarding international law, blockades are quite legal. The United States and Britain were at war with Germany and Japan and blockaded them. I can't remember international lawyers saying those blockades were illegal—even though they took place on the high seas in international waters. There would be a general violation only if the hostile actions against the ships took place in waters under the jurisdiction of another sovereign state. Thus, for example, if the Israelis stopped the ships in Egyptian waters, that would have been a violation.