NATO Interdiction of Oil Tankers Bound for Yugoslavia

Frederic L. Kirgis
April 02, 1999
NATO is preparing to interdict deliveries by sea of refined oil bound for Yugoslavia, as a means of ensuring that NATO's bombing of Serbian oil refineries will not be neutralized by the supply of refined oil from other sources.  France and Italy have raised a question whether such interdiction at sea would violate international law. 
International law provides that ships on the high seas are subject to the exclusive jurisdiction of the flag state, with very few exceptions.  Ships passing through territorial waters are also entitled to be left alone, so long as they are in innocent passage.  Delivery of oil and other goods on merchant ships would normally be an exercise of the right of innocent passage.  Even if passage were not innocent in a particular instance, only the coastal state would normally have the right to interrupt it in its territorial waters. 
Traditionally, these rules have been subject to some exceptions in time of war.  The navy of a combatant state could blockade the ports of an enemy state, if the blockade was applied to all ships and was effective.  NATO does not contemplate a blockade of all ships. 
A combatant could also interdict contraband at sea, even without a full-scale blockade.  The clearest form of contraband, "absolute contraband," consists of arms, ammunition and other purely military equipment.  These items could be interdicted in wartime.  "Conditional contraband" includes oil and other items that could have civilian as well as military uses, and could be interdicted only if destined for the military.  Pentagon officials reportedly are relying on the right to intercept contraband in time of armed conflict, as one of the legal justifications for the planned NATO action at sea. 
The traditional law of blockade and contraband developed in a time when international law had little to say about the circumstances under which the use of armed force was or was not justifiable.  With the advent of the United Nations Charter in 1945, the use of armed force became legally justifiable only under certain circumstances, such as proportional self-defense (individual or collective) against armed attack, enforcement action if authorized by the U.N. Security Council, and perhaps limited forms of humanitarian intervention.  It is doubtful that the traditional right of blockade or seizure of contraband from ships flying the flag of a noncombatant state survived into the U.N. era, unless the use of armed force is itself legally justifiable under the circumstances just mentioned.  The principal legal arguments in support of NATO's use of armed force against Serbia are based on extensions of collective self-defense and humanitarian intervention.  (For fuller exposition of the legal issues regarding NATO's use of armed force against Serbia, see the ASIL Flash Insight of March 25, 1999, and the responses thereto on the ASIL web site, <>.) 
In March 1998 the Security Council, acting under Chapter VII of the U.N. Charter, imposed an embargo on the supply to Yugoslavia of "arms and related matériel of all types, such as weapons and ammunition, military vehicles and equipment and spare parts for the aforementioned."  S.C. Res. 1160.  The Council called on all states and regional organizations to act strictly in conformity with the resolution and created a committee to monitor compliance, but did not expressly authorize NATO or any states to enforce it.  Like other legal instruments, however, the resolution is subject to interpretation.  Pentagon officials reportedly are relying on it, as well as on the law relating to contraband, as authority for NATO interdiction of oil supplies bound for Serbia. 
In recent years the Security Council has imposed comprehensive trade embargoes on Iraq, and on Serbia-Montenegro during the Bosnian conflict, and has later expressly authorized states to take the necessary measures to make the embargoes effective.  Those authorizations under the Council's Chapter VII powers have trumped the rights of flag states to have their merchant ships be free from boarding at sea, so long as the interdicting ships were simply acting to enforce the Council's embargoes.  It was not necessary to rely on traditional rights of blockade or seizure of contraband, since the Council had legitimated the interdictions.  The questions France and Italy have raised about the current plan to interdict oil shipments to Serbia are that the Council has not expressly embargoed such oil shipments and has not expressly authorized interdiction, so the planned NATO action may be vulnerable on international law grounds insofar as it is to be carried out against ships flying the flags of non-NATO countries that object to the interdiction. 
Further Views
Oil Blockade Threatens International Law of the Sea (published by Reuters April 28, 1999)
Philippe Sands
April 1999
Over the past few days NATO has decided to adopt a maritime "blockade" on supplies of oil to Yugoslavia. This would violate basic rules of international maritime law, a fact that, with the exception of France, no NATO member appears troubled by. If what is proposed is simply to impose the prohibition on oil supplied by NATO and EU registered vessels, then there would appear to be little difficulty. If, as it appears, it is proposed to impose and then enforce a unilateral prohibition against non-NATO and non-EU vessels seeking to supply oil - including stop and search of these vessels on route - then new and troubling legal questions are raised, as recognised by NATO General Klaus Naumann on Monday. 
One of the most basic principles of international law is freedom of maritime navigation: the freedom of one state's vessels to ply their trade on the high seas (and innocently through the waters of other states, including straits) without hindrance or interference by other states. High seas and related freedoms are now codified in the United Nations' 1982 Convention on the Law of the Sea, which is generally considered to reflect customary international law, and to which the United Kingdom and 129 other states, including Yugoslavia and Russia, are party. The 1982 Convention generally prohibits a warship from one state from visiting or boarding a foreign ship on the high seas. There are a number of exceptions, relating for instance to piracy and slavery, none of which apply here. An interception carried out in the Straits of Otranto, through which Yugoslav-bound oil must pass, appears equally difficult to justify. Ironically, it was in respect of the same general waters that in 1949 the United Kingdom brought - and won - against Albania the very first case heard by the International Court of Justice, successfully arguing that innocent passage through straits is a right recognised by international law. 
The law has not materially changed in the intervening fifty years. So a right to impose and enforce an oil blockade on the high seas or in the Straits of Otranto could be justified if based on an international treaty right - for example the United Nations Charter, or action taken by the UN Security Council under the Charter. However, the only Security Council resolution which appears remotely relevant to justify interceptions is resolution 1160, which was adopted on 31 March 1998. By that resolution the Security Council adopted a prohibition on sales of military equipment to Yugoslavia: "all States shall ... prevent the sale or supply to the Federal Republic of Yugoslavia, including Kosovo, by their nationals or from their territories or using their flag vessels and aircraft, of arms and related materiél of all types, such as weapons and ammunition, military vehicles and equipment and spare parts for the aforementioned". The resolution makes no mention of oil. It provides no basis for an oil embargo because the typical definition of "materiel" does not include oil. In the past, when the Security Council has wanted to ban oil supplies it has done so in express terms, for example in relation to Iraq. To treat oil as "materiel" here would severely undermine the prospects for future Security Council resolutions, because it would suggest that Security Council terms may be unilaterally rewritten once adopted. 
NATO's actions thus far are at least plausibly lawful, by reference to the emerging principle of "humanitarian intervention". This posits that states are not required to stand idly by as massive (and arguably genocidal) violations of human rights take place within the territory of another state. They are arguably entitled to take steps against the state perpetrating the massive violation of human rights. But even here other questions must be addressed. Why was no effort made to obtain prior authorisation of the Security Council? Why were similar measures not taken five years ago in the context of Bosnia? And why are the measures now being utilised not better designed to provide the humanitarian benefits they purport to promote, at least in the short term? If there is to be a new "Blair doctrine" justifying "humanitarian intervention" it must be based upon principles which are clearly articulated and objectively applied in the context of sound legal principles. 
A unilateral oil "blockade" enforced against third states would not be based on sound legal principles and would constitute a significant escalation. We should care whether the enforcement of such a "blockade" is or is not legal because the stability of international relations is best served by complying with the international rule of law. In the case of the law of the sea, there are additional, self-interested reasons for the most stringent and careful application of the rules. As a seafaring nation Britain benefits significantly from the rules now enshrined in the Law of the Sea Convention. They were negotiated over a period of nearly twenty years, and have achieved broad support. Amongst other matters, these rules are the backbone of Britain's international trade, its high seas fisheries activities, and its extensive programme of maritime research. The Convention's rules were also carefully designed to allow naval powers such as Britain to continue to exercise a naval presence at great distances from home. If NATO starts re-writing the rules where short-term expediency suits there is every probability that other exceptions - which are not found in the Convention - will be created and relied upon in other contexts. If NATO's actions are to continue to attract support, they must at the very least be premised upon plausible legal arguments. The imposition of an oil "blockade" against third states without their consent does not meet this standard. 
About the Author:  Philippe Sands is a practising barrister and Reader in International Law at the University of London (School of Oriental and African Studies).