The Global Sumud Flotilla said Tuesday that over 15 drones circled low above one of its boats for hours, describing it as both an intimidation tactic and a potential intelligence operation by Israel, a day after it announced that it would not allow the humanitarian aid ship to break its illegal blockade.

The flotilla said the drones appeared "roughly every 10 minutes” over a ship called the Alma, which is part of the convoy aiming to reach Gaza and challenge Israel’s illegal blockade.

"We believe these drones are intended to intimidate, potentially gathering intelligence for Israel,” the group said.

The flotilla, which includes dozens of boats, is sailing in international waters with humanitarian aid bound for Gaza.

The Global Sumud Flotilla, also carrying prominent pro-Palestinian advocates including Swedish climate activist Greta Thunberg, set sail for Gaza earlier this month from Tunisia after repeated delays.