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.
4 UN peacekeepers injured in Sinai and taken to hospital in south Israel (Haaretz)
from the article: Israel releases arms ship said destined for Hezbollah