PM Erdogan of Turkey said, speaking of Israel’s raid on the Mavi Marmara, in an interview on Al Jazeera last week:
The attack that took place in international waters did not comply with any international law. In fact, it was grounds for war.
Other than being dimwitted, which I cannot imagine Erdogan is, the only possible way that he could argue the first portion of this is if he ignores what international law actually says. If a blockade is legal, and the UN says that it is according to the Palmer Report, than any vessel declaring intent to run the blockade is a legal target no matter where it is on the seas. See Talk Gaza Flotilla for a good analysis of the legal issues, but here is the most important:
The San Remo Manual on International Law Applicable to Armed Conflicts at Sea (12 June 1994). S67 states that “Merchant vessels flying the flag of neutral States may not be attacked unless they: (a) are believed on reasonable grounds to be carrying contraband or breaching a blockade, and after prior warning they intentionally and clearly refuse to stop, or intentionally and clearly resist visit, search or capture.
This is why the Palmer Commission found Israel’s raid legal. Israel complied with every bit of this. As for the international waters argument, clearly the Palmer Commission didn’t buy it either because it is legal to confront a ship known to be “breaching a blockade” end of story.
Thus, the casus belli. Well, a country enforcing a legal blockade acting to enforce that blockade legally can hardly be accused of a casus belli. However, a nation knowingly backing ships whose goal it is to breach a blockade certainly could be accused of one and beyond any doubt, escorting such vessels would be considered a casus belli, a cause for war.
Right now, we have many nations condemning Israel for not apologizing for acting legally, though perhaps more harshly than it could have. Perhaps. But who is condemning Turkey for threatening war? Turkey has a lot to offer and like Saudi oil, that is allowing it a free pass.