There are clear laws on enforcing blockades – Israel’s interception of the Madleen raises serious questions

On June 9, the Madleen, a UK-flagged civilian ship carrying humanitarian aid to Gaza, was stopped by Israeli forces in international waters, about 200 kilometres off the coast.

The Freedom Flotilla Coalition had organised the voyage, setting sail from Sicily on June 1. The vessel’s 12 passengers included climate activist Greta Thunberg, European Parliament member Rima Hassan, two French journalists and several other activists from around the world.

The Israeli military boarded the ship and diverted it to the Israeli port of Ashdod. The aid it carried — baby formula, food, medical supplies, water desalination kits — was confiscated. All passengers were detained and now face deportation.

This interception has sparked international condemnation. Importantly, it also raises questions about whether Israel’s actions comply with international law.

Legal conditions for naval blockades

Naval blockades are not automatically illegal. Under the San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1994), a blockade may be used in wartime, but only if five legal conditions are met:

• it must be formally declared and publicly notified
• it must be effectively enforced in practice
• it must be applied impartially to all ships
• it must not block access to neutral ports or coastlines
• it must not stop the delivery of humanitarian aid to civilians.

If even one of these conditions is not met, the blockade may be considered illegal under customary international humanitarian law.

The fifth condition is especially important here. According to a comprehensive study of international humanitarian law conducted by the International Committee of the Red Cross, the parties to a conflict must allow the rapid and unimpeded delivery of humanitarian relief to civilians in need.

A blockade that prevents this could be in breach of international law.

Israel and Egypt have imposed a blockade of varying degrees on Gaza since 2007 when Hamas came to power. Israeli Defence Minister Israel Katz claims the purpose of the blockade is to “prevent the transfer of weapons to Hamas”. Critics say it amounts to collective punishment.

The Madleen was operating in compliance with three binding International Court of Justice orders (from January 2024, March 2024 and May 2024) requiring unimpeded humanitarian access to Gaza.

Freedom of navigation

International law also strongly protects the freedom of navigation, particularly in international waters beyond any state’s territorial limits.

There are only a few exceptions when a country can lawfully stop a foreign ship in international waters – if it is involved in piracy, slave trading, unauthorised broadcasting, or the vessel itself is stateless. A country can also stop a ship if it is enforcing a lawful blockade or acting in self-defence under Article 51 of the UN Charter.

So, if Israel’s actions do not fully meet the international legal requirements for enforcing a blockade during wartime, it would not have the right to intercept the Madleen in international waters.

Protections for humanitarian workers

More broadly speaking, international humanitarian law, including the Fourth Geneva Convention, protects civilians during conflict. This protection extends to people delivering humanitarian aid, so long as they do not directly take part in hostilities.

To be considered directly participating in hostilities, a person must:

• intend to cause military harm
• have a direct causal link to that harm, and
• be acting in connection with one side of the conflict.

Bringing aid to civilians, even if politically controversial, does not meet this legal threshold. As a result, the Madleen’s passengers remain protected civilians and should not be treated as combatants or detained arbitrarily.

International law also sets out how civilians detained in conflict situations must be treated. Under the Fourth Geneva Convention, detainees must be given access to medical care, lawyers and consular representatives. They must also not be punished without fair legal processes.

Reports that Madleen passengers have been detained and are facing deportation raise concerns about whether these standards are being upheld.

In response to the ship’s interception, the Hind Rajab Foundation, a nonprofit advocacy group, has filed a complaint with the UK Metropolitan Police War Crimes Unit. The complaint alleges a number of breaches of international humanitarian law, including forcible detention, obstruction of humanitarian relief, and degrading treatment.

Previous flotilla intercepted

This is not the first time Israel has stopped an aid ship and faced accusations of violating the law of the sea and humanitarian law.

In 2010, the Israeli military raided a flotilla of six ships organised by international activists aiming to deliver humanitarian aid to Gaza and challenge the blockade.

Violence broke out on the largest vessel, the Mavi Marmara, resulting in the deaths of nine Turkish nationals and injuries to dozens of others. The incident drew international condemnation. Israel agreed to ease its blockade after the incident.

A fact-finding mission established by the UN Human Rights Council found that Israel violated a number of international laws and that its blockade was “inflicting disproportionate damage upon the civilian population”.

This is not just a political or moral issue – it’s a legal one. International law lays out clear rules for when and how a country can enforce blockades, intercept vessels and treat civilians.

Based on these rules, serious legal questions remain about Israel’s handling of the Madleen and its passengers.