Israel was justified in its May 31 sea battle according to Section 5, clause 67 (a) of the San Remo Manual of International Law.

The law states:

67: 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;