An aid flotilla of dozens of boats that had set sail for Gaza on Sunday carrying aid and pro-Palestinian activists, including climate campaigner Greta Thunberg, has returned to port in Barcelona due to stormy weather, organisers said on Monday.

“We conducted a sea trial and then returned to port to allow the storm to pass. This meant delaying our departure to avoid risking complications with the smaller boats,” the Global Sumud Flotilla Mission said in a statement, adding winds had been up to around 35 mph (56 kph).

The organizers did not say when they planned to resume the journey.

Activists including Game of Thrones actor Liam Cunningham are on the flotilla of several dozen boats that is aiming to break Israel’s naval blockade and deliver food and humanitarian supplies to the enclave, which has been devastated by nearly two years of war.

Israel has argued that the naval blockade it imposed in 2007 is necessary to stop weapons being smuggled to the Hamas Palestinian militant group.

It has described other attempts to break it - including one that included Thunberg in June - as a propaganda stunt in support of Hamas.