Organizers of a Gaza-bound flotilla carrying humanitarian aid and pro-Palestinian activists reported that several of their boats were targeted by multiple drones on Wednesday.

The Global Sumud Flotilla announced that over a dozen explosions were heard as it sailed off the coast of Greece late Tuesday, with damage attributed to “unidentified objects” dropped onto the vessels.

The flotilla reported incidents of communications being jammed and explosions occurring from several boats. Polish lawmaker Franek Sterczewski, onboard one of the vessels, stated that there had been 13 attacks on a total of 10 boats, resulting in damage to three ships.

German human rights activist Yasemin Acar, another member of the flotilla, emphasized in a video that their mission was solely to deliver humanitarian aid, asserting they carried no weapons and posed no threat. She condemned Israel for the ongoing violence and humanitarian crisis in Gaza.

In an earlier video, Acar mentioned sighting 15 to 16 drones and reported that their radios had been jammed amid loud music. One video shared by the flotilla captured an explosion from the vessel Spectre at 0143 GMT.

The Greek coastguard stated that a European Union borders agency (Frontex) patrol boat inspected one of the vessels and found no evidence of damage.

A coastguard spokeswoman confirmed that the coastguard operations room was informed of the incident after 2:30am but could not determine if it occurred in international waters.

In another video, Brazilian activist Thiago Avila reported that four boats had been targeted by drones just before an explosion was heard. The Global Sumud Flotilla, which set sail from Barcelona earlier this month, aims to break the Israeli blockade of Gaza and deliver aid. Currently, it comprises 51 vessels, most of which are near the Greek island of Crete.

The flotilla had previously faced drone attacks while waiting to depart from Tunisia, where Swedish climate activist Greta Thunberg was among those who joined. Israel has stated that it will not permit the flotilla to reach Gaza, amidst escalating international pressure regarding its military actions in the region.