@oralloy,
Since you seem to want to doubt me, lets look at exactly what the law says...
http://www.admiraltylawguide.com/conven/unclospart2.html
start reading at section 3 article 19 subsection 2(g)
That part is the part that gives Israel the right to stop and search those ships, WITHIN Israeli territorial waters.
Now, they also can legally stop ships in the contiguous zone, outside of their territorial waters.
So, lets look at what the UNCLOS says about that.
To find out what that is, just read section 4.
It is very clear about what the contiguous zone is, and what Israel can legally do in that zone.
Now what you are talking about is a military blockade, in a time of war.
The UNCLOS does not apply then, the rules of war apply.