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.

It aims to break Israel's siege of Gaza and deliver aid to the territory.

Prior to its departure, it said that two of its boats were targeted by drone attacks.

Israel blocked two earlier attempts by activists to reach Gaza by sea in June and July.

The initiative unites four movements: the Maghreb Sumud Flotilla, the Global Movement to Gaza, the Freedom Flotilla Coalition and Sumud Nusantara.

Rejecting international calls for a cease-fire, Israel has continued its military offensive on Gaza since Oct. 7, 2023, killing over 65,000 Palestinians, almost half of them women and children. The campaign has devastated the territory and pushed it to the verge of famine.

Last November, the International Criminal Court issued arrest warrants for Israeli Prime Minister Benjamin Netanyahu and former Defense Minister Yoav Gallant on war crimes and crimes against humanity charges. Israel also faces a genocide case at the International Court of Justice.