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Blockade, aggression, and jus cogens: Why Trump’s restriction on Venezuela’s oil tankers tests the limits of international law | The Leaflet

International Law & World Affairs Opinion

Blockade, aggression, and jus cogens: Why Trump’s restriction on Venezuela’s oil tankers tests the limits of international law

The US blockade of Venezuela implicates aggression, self-defence, and the prohibition on the use of force under international law.

Atul Alexander

Published on: 30 December 2025, 12:10 am

Blockade, aggression, and jus cogens: Why Trump’s restriction on Venezuela’s oil tankers tests the limits of international law

ON DECEMBER 16, the United States (US) announced measures to block oil tankers entering and leaving Venezuela. The Trump administration alleges that Nicolás Maduro’s regime is engaged in drug trafficking and human trafficking. The U.S has expanded its naval presence in the region, ostensibly to interrupt the drug-smuggling boat.

According to TankerTrackers.com, more than 30 out of 80 vessels in Venezuelan waters or approaching Venezuela are under US sanctions. Over time, Trump's position has shifted from allegations of drug trafficking to claims that the Maduro government is using stolen oil to finance, what he terms, “drug terrorism” and human trafficking. In response, Venezuela has accused Washington of illegally expropriating its resources.

Considering Venezuela’s over-dependence on oil, the move carries far-reaching geopolitical implications. China has expressed its displeasure over the “unilateral bullying,” and Mexico has urged the United Nations to intervene to diffuse the tensions. Meanwhile, Deputy Chief of Staff Stephen Miller claimed in a post on Xt that the “tyrannical expropriation” by Venezuela amounted to “the largest recorded theft of American wealth and property.” Joaquin Castro, a Democrat from Texas, has termed these measures “an act of war.” Maduro has characterized the move as an attempt at regime change and an assertion of US control over Venezuelan territory and resources.

The total blockade by the US has left the scholars divided. According to NYU professor Ryan Goodman, “[t]here is no legal justification for a military blockade based on the grievances President Trump listed.” Writing for Just Security, Michael Schmitt and Rob McLaughlin argue that the US actions amount to a threat or use of armed force against oil tankers entering or leaving the territorial waters of Venezuela. They characterise blockade as the use of force, even prior to the actual use of force under Article 42 of the UN Charter, which expressly lists blockade as a coercive measure when non-forcible means have failed. They further argue that a blockade constitutes aggression within the meaning of United Nations General Assembly (UNGA) Resolution 3314.

A ‘peacetime blockade’ would qualify as a use of force even before any kinetic engagement with the ships, since Article 42 of the UN Charter provides for blockade as a measure which the UNSC can authorise when non-forceable actions fail. By implication, the unilateral imposition of a blockade, without the UNSC’s authorisation, breaches the prohibition on the use of force.

US officials have justified these actions on grounds of self-defence, a claim decipherable from Trump’s Truth Social post in the face of the drug threat. However, the shift in Trump’s position from interdicting drug-boats to claims over oil and other assets significantly weakens any claim of self-defence. Additionally, for invoking self-defence, the threshold of ‘armed attack’ is high; for instance, in the Nicaragua case, the ICJ categorised an armed attack as “the most grave” form of the use of force. On this reasoning, the US blockade would itself constitute a grave use of force, and potentially trigger Venezuela's right to self-defence. Finally, blockade cannot be justified on political, economic, military, or any other grounds, as affirmed by UNGA Resolution 3314.

Aggression as a violation of jus cogens

Jus cogens are peremptory norms of international law from which no derogation is permitted. In the hierarchy of norms, these are placed higher than treaties and customary international law. Scholars like Katie A. Johston and Corten identify prohibition of aggression as a jus cogens norm. Aggression is commonly used alongside the unlawful use of force, but its classification depends on the gravity and character of the force employed. In this context, in the Oil Platforms case, the ICJ did not exclude the possibility that the mining of a military vessel might be sufficient to bring into play the “inherent right of self-defence.”

Similarly, the blockade of the port of Mariupol and the Sea of Azov was regarded as constituting aggression; accordingly, scholars like James A. Green et al. regard the invasion of Ukraine as an act of aggression and a violation of jus cogens. Several authoritative international instruments identify aggression as a jus cogens norm. For instance, the International Law Commission’s (ILC) Draft Conclusion on Identification and Legal Consequences of Peremptory Norms of General International Law (jus cogens) in its non-exhaustive list locates prohibition on aggression as jus cogens; likewise, the ILC report on fragmentation identifies prohibition on aggression as the most frequently cited candidate for jus cogens status.

Accepting the US-Israeli position on the Iran strikes would erode the moral permissibilities of international law

First, the supreme status of the prohibition of aggression as a jus cogens norm would entail an obligation erga omnes, wherein States not directly affected by the acts of the US could bring claims against it. This could be achieved through third-party countermeasures (sanctions) or by taking the US to the International Court of Justice. Furthermore, domestic jurisdictional claims would be strengthened if the prohibition on aggression were categorised as jus cogens, as States like Germany, Ukraine, and Switzerland have criminalised aggression in their domestic laws.

Second, States cannot be precluded from responsibility for jus cogens breaches. As Article 26 of the ILC Draft Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA) states: “Nothing in this chapter precludes the wrongfulness of any act of a State which is not in conformity with an obligation arising under a peremptory norm of general international law.” As Norman Finkelstein notes, “we’re upping the ante in order to try to get them to engage in an act of aggression that would then justify an act of self-defence on our part.” Further, the Pentagon officials view the blockade as a “quarantine,” a language employed during the 1962 Cuban Missile Crisis to cordon off weapon shipments from the Soviet Union. Such framing does not, however, alter the legal character of the act under international law. Hence, any justification, like self-defence, cannot be used to justify a blockade.

The ICJ’s position on self-defence for acts of aggression is evident in the Nicaragua case. There, the US attempted to justify collective self-defence for Nicaragua’s alleged aggression against El Salvador, Honduras, and Costa Rica; the argument was dismissed, as El Salvador’s request was not supported by an armed attack capable of triggering self-defence.

Jus cogens are peremptory norms of international law from which no derogation is permitted. In the hierarchy of norms, these are placed higher than treaties and customary international law.