Barcelona (AFP) – Fierce Mediterranean winds forced a Gaza-bound flotilla carrying humanitarian aid and hundreds of pro-Palestinian activists, including environmental campaigner Greta Thunberg, to return to Barcelona, organisers said on Monday.

Around 20 vessels left the Spanish city on Sunday aiming to “open a humanitarian corridor and end the ongoing genocide of the Palestinian people” amid the Israel-Hamas war, said the Global Sumud Flotilla – sumud being the Arabic term for “resilience”.

But “due to unsafe weather conditions, we conducted a sea trial and then returned to port to allow the storm to pass,” the organisation said in a statement, without specifying when exactly the boats returned to Barcelona.

“This meant delaying our departure to avoid risking complications with the smaller boats,” it added, citing gusts that exceeded 55 kilometres (34 miles) per hour.

“We made this decision to prioritize the safety and well-being of all participants and to safeguard the success of our mission.”

Spanish media reported that the organisers would meet to decide whether to resume the expedition later on Monday.

Among the activists from dozens of countries were Thunberg, actors Liam Cunningham of Ireland and Eduard Fernandez of Spain, as well as European lawmakers and public figures, including former Barcelona mayor Ada Colau.

The flotilla is expected to arrive in Gaza in mid-September and comes after Israel blocked two activist attempts to deliver aid to the devastated Palestinian territory by ship in June and July.