A vessel taking part in a humanitarian flotilla to Gaza was struck by what organizers said was an incendiary device dropped from a drone while docked near Tunis, according to the group that organized the mission. Tunisia’s interior ministry disputed that account, saying a fire was caused by a lighter or a cigarette butt.

The Global Sumud Flotilla (GSF) said the incident occurred just after midnight local time on Tuesday at the Sidi Bou Said port and that videos posted on social media showed an object dropped from above and subsequent burn damage on the main deck. The vessel, identified by GSF as the Family Boat and sailing under a Portuguese flag, had six passengers and crew aboard; the group said all were safe and unharmed. Protesters gathered at the port following the event.

GSF, which organized the mission to carry humanitarian aid to Gaza and said it aims to challenge Israel’s blockade, set off from Barcelona last week and arrived in Tunisia on Sunday. Greta Thunberg, the Swedish climate activist who has participated in prior flotilla actions, was among a number of activists associated with the broader movement in recent months. In June, a separate Freedom Flotilla Coalition ship that included Thunberg was intercepted and its passengers detained off the coast, taken to Israel and later deported.

Tunisia’s interior ministry issued a statement saying reports that a drone struck the boat "have no basis in truth," and that an initial investigation indicated the fire was caused by a lighter or a cigarette butt. The statement did not say whether the ministry had examined the video footage posted by the flotilla organizers. The United Nations special rapporteur for the occupied Palestinian territories, Francesca Albanese, who is based in Tunis, suggested Israel may have been behind the attack but provided no evidence. The Israeli Foreign Ministry did not immediately respond to a request for comment.

Organizers of past flotillas have pointed to a history of confrontations at sea. In 2010, 15 Turkish activists were killed on board the Mavi Marmara after Israeli forces intercepted a flotilla bound for Gaza. Activists and organizers have framed the GSF mission as a civilian effort to deliver aid and to challenge what they call an unlawful blockade; Israeli officials have defended maritime interdictions as measures tied to security and restrictions on the entry of weapons.

The incident in Tunis unfolded as hostilities in Gaza have prompted further displacement orders from the Israel Defense Forces. On Tuesday the IDF issued evacuation orders for the entirety of Gaza City and advised residents to move to the Al Mawasi humanitarian zone near the southern coast, saying it would operate in the area with "great force." Aid groups and the U.N. have warned that repeated evacuation orders and ongoing fighting are producing increasingly dire humanitarian consequences.

"The Al Mawasi area is totally filled with people already. The coast is very expensive to find accommodation, and people may not be able to afford to leave their homes in Gaza City to move down to the south and find adequate shelter," said Mai Elawawda, communications officer for Medical Aid for Palestinians. She said dozens of Palestinians had arrived in the area from northern Gaza on Tuesday morning without tents.

The U.N. Office for the Coordination of Humanitarian Affairs said that many households are unable to move because of high costs and a lack of safe space, with older people and those with disabilities especially affected. OCHA said 82,000 new displacement orders were issued between Aug. 14 and Aug. 31 and warned of "horrific humanitarian consequences" if displacement continues and hostilities intensify.

Organizers of the Global Sumud Flotilla said the Tunis incident will not deter their efforts to deliver aid to Gaza, and called for international scrutiny of what they described as attacks on civilian ships attempting to reach the Strip. Tunisian authorities said they would continue their investigation into the cause of the fire aboard the Family Boat.

International responses were limited on Tuesday, with activists, U.N. officials and Tunisian authorities offering differing accounts while independent verification of the source of the device was not publicly available. The flotilla's organizers posted video and images of the damage online; journalists and investigators have sought additional material to corroborate competing claims as aid agencies monitor both sea routes and ground conditions in Gaza amid growing displacement and humanitarian need.