A Gaza-bound activist aid ship caught fire and issued an SOS, after what its organizers claimed was a drone attack off the coast of Malta in international waters in the early hours of Friday.

The Freedom Flotilla Coalition (FFC), which is campaigning to end Israel’s blockade of Gaza, told CNN activists were aboard its ship carrying humanitarian aid when the alleged attack happened just after midnight local time (6 p.m. ET Thursday).

“There is a hole in the vessel right now and the ship is sinking,” Yasemin Acar, the coalition’s press officer, told CNN by phone from Malta on Friday morning.