The ship was not boarded by the UN or any other recognized authorized organization but by a bunch of terrorists from a rogue state itself in contravention of numerous UN resolution. The same Israelis who slaughters unarmed women and children at point blank range and shoots caged animlas in a zoo. Israel has as much rights as the Somalian pirates to board and confiscate vessels and cargo in Int.Waters.
Man shot dead in northern Israel town of Bi'ina, police say the murder was gang related (Haaretz)
from the article: Israel releases arms ship said destined for Hezbollah