Haaretz writes: "IDF Navy forces boarded the Scandinavian Gaza-bound Estelle ship attempting to breach Israel's blockade on the Strip. Control over the ship was seized in Israeli territorial waters, as the IDF maintained its forces acted in accordance with the international law." Estelle was attacked in waters southwest of Gaza. That could not be Israeli waters, and accordingly it is against international law.
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from the article: Israel Navy intercepts pro-Palestinian activist ship off Gaza coast