Organizers of a pro-Palestinian flotilla, hoping to carry much-needed humanitarian aid to Gaza, said Tuesday that one of their boats was targeted by an Israeli drone attack off the coast of Tunisia.

The Global Sumud Flotilla, which set off from Barcelona last week with hundreds of activists on board, including Greta Thunberg, said one of its main boats was "struck by a drone in Tunisian waters."

"All six passengers and crew are safe," the statement added. "Fire damage was caused to the main deck and below-deck storage."

Tunisian authorities have rejected claims of a drone attack and said a fire on board was caused by a burning life jacket.

Citing the Interior Ministry, the Tunisian state news agency TAP reported that security forces investigated the fire on board and determined that it started from a burning life jacket.

There were no casualties or damage to property, apart from several burnt life jackets, the agency said.

However, the flotilla published videos on Instagram showing a flash emerging from the sky and hitting the boat, causing a fire.

Francesca Albanese, the U.N. special rapporteur on the occupied Palestinian territories, said the incident had caused "shock" and warned that the flotilla had faced threats, including from Israel.

She highlighted the "history of attacks on the flotilla."

Organizers plan to provide information about the reported incident at a press conference today.

The Global Sumud Flotilla is aiming to breach the Israeli sea blockade of the Gaza coast to deliver humanitarian aid to the population of the war-torn territory. "Sumud" means steadfastness in Arabic.