The San Remo Manual on International Law Applicable to Armed Conflicts.
Specifically paragraph 98:
98. Merchant vessels believed on reasonable grounds to be breaching a blockade may be captured.
Merchant vessels which, after prior warning, clearly resist capture may be attacked.
The San Remo Manual on International Law Applicable to Armed Conflicts. Specifically paragraph 98:
98. Merchant vessels believed on reasonable grounds to be breaching a blockade may be captured. Merchant vessels which, after prior warning, clearly resist capture may be attacked.