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Convention on Maritime Neutrality. Havana, 20 February 1928.
Section III : Rights and duties of neutrals - Art. 21.
Art. 21. Should it be found that a merchantman flying a belligerent flag, by its preparations or other circumstances, can supply to warships of a state the stores which they need, the local authority may refuse it supplies or demand of the agent of the company a guaranty that the said ship will not aid or assist any belligerent vessel.