Relevant Articles from the San Remo Manual on International Law Applicable to Armed Conflicts at Sea
118. In exercising their legal rights in an international armed conflict at sea, belligerent warships and military aircraft have a right to visit and search merchant vessels outside neutral waters where there are reasonable grounds for suspicion that they are subject to capture.
119. As an alternative to visit and search, a neutral merchant vessel may, with its consent, be diverted from its declared destination.
121. Neutral merchant vessels are subject to capture outside neutral waters if they are engaged in any of the activities referred to in paragraph 67 or if it is determined as a result of visit and search or by other means, that they:
(a) Are carrying contraband;
(b) Are on a voyage especially undertaken with a view to the transport of individual passengers who are embodied in the armed forces of the enemy;
(c) Are operating directly under enemy control, orders, charter, employment or direction;
(d) Present irregular or fraudulent documents, lack necessary documents, or destroy, deface or conceal documents;
(e) Are violating regulations established by a belligerent within the immediate area of naval operations; or
(f) Are breaching or attempting to breach a blockade.
Capture of a neutral merchant vessel is exercised by taking such vessel as prize for adjudication.
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;
* San Remo Manual on International Law Applicable to Armed Conflicts at Sea, 12 June 1994, prepared by international lawyers and naval experts convened by the International Institute of Humanitarian Law, published by Cambridge University Press. The manual is not a legally binding document, but is considered, in most parts, reflecting customary international law.