Israeli naval forces intercepted a Gaza-bound aid flotilla early Thursday, detaining several passengers including Swedish climate activist Greta Thunberg, organizers and Israeli officials said. The flotilla, organized by the Global Sumud coalition, was en route from Cyprus with medical supplies and non-perishable aid intended for Gaza when it was stopped in international waters north of the besieged territory, according to both sides.

A pre-recorded video statement from Ms. Thunberg was released by her campaign team shortly after news of the interception became public. “If you are seeing this, I have been detained while trying to deliver aid and attention to a humanitarian crisis,” she said. “I oppose violence in all forms and demand safe passage for humanitarian assistance and the protection of those who seek to help.” The message called for nonviolent action and for international observers to be allowed to verify the treatment of detainees.

The Israeli Defense Forces (IDF) said in a written statement that its naval units intercepted the vessels after attempts to coordinate delivery of goods to Gaza through established humanitarian channels had failed. “For security reasons and to prevent weapons smuggling, our forces boarded the flotilla and detained individuals for questioning,” an IDF spokesperson said. The statement added that aid will be inspected and that civilians detained would be treated in accordance with Israeli and international law.

Global Sumud organizers sharply disputed Israel’s characterization, saying the flotilla carried only civilian medical supplies and food, and that the interception was an unlawful use of force. “This was peaceful humanitarian action,” said Lina Haddad, a coordinator for the mission. “Detaining activists, journalists and aid workers will not stop us from drawing attention to Gaza’s dire needs.”

The encounter raises immediate legal and diplomatic questions. International maritime law allows interdiction in certain circumstances, but legal scholars note that blockades and naval boardings must comply with the San Remo Manual and other rules of armed conflict, including safe treatment of civilians and unimpeded humanitarian relief. “Even where a state asserts security concerns, it must facilitate impartial humanitarian assistance,” said Professor Miriam Al-Hassan, an expert in international humanitarian law at the University of Amsterdam.

Governments and rights groups reacted quickly. Sweden’s foreign ministry said it had summoned the Israeli ambassador and requested consular access to Ms. Thunberg. The United Nations Office for the Coordination of Humanitarian Affairs called for transparency and unhindered delivery of aid to Gaza, while Amnesty International described the interception as “a dangerous escalation” if peaceful activists and humanitarian cargo were impeded.

The incident is likely to intensify protests across Europe, where anti-war and pro-Palestinian demonstrations have grown since Israel’s military operations in Gaza. It also places European governments in a delicate position: balancing relations with Israel on security grounds against pressure from domestic constituencies and international law advocates.

For Ms. Thunberg, already a polarizing global figure, the detainment — and the strategic release of a pre-recorded statement — amplifies her campaign tactics while thrusting climate activism into another geopolitical flashpoint. How governments and international bodies respond will test the norms governing humanitarian access at sea and may have lasting repercussions for civil society efforts to challenge blockades and spotlight civilian suffering.