(BSS/AFP) - The organisers of a Gaza-bound flotilla carrying humanitarian aid and pro-Palestinian activists said late Monday that one of their boats was hit by a suspected UAV but Tunisian authorities said "no drones" had been detected.

The flotilla, which aims to deliver aid to Gazans in defiance of Israel`s blockade, arrived in Tunisia over the weekend and was anchored 50 miles from the port of Sidi Bou Said when it reported the incident.

"The Global Sumud Flotilla (GSF) confirms that one of the main boats... was struck by what is suspected to be a drone," the organisers said on social media, adding no one had been hurt.

The boat was in Tunisian waters when a fire broke out onboard and was quickly extinguished, according to an AFP journalist who arrived shortly after the flames had been doused.

Houcem Eddine Jebabli, a spokesman for Tunisia`s national guard, said their investigation was "ongoing" but "no drones have been detected".

"According to preliminary findings, a fire broke out in the life jackets on board a ship anchored 50 miles from the port of Sidi Bou Said," he said.

Reports of a drone are "completely unfounded", the national guard said in a statement on its official Facebook page, suggesting that the fire may have been caused by a cigarette.

The Global Sumud Flotilla describes itself as an independent group not linked to any government or political party. Sumud means "resilience" in Arabic.

Among its high-profile participants is Greta Thunberg, who addressed pro-Palestinian campaigners in Tunisia on Sunday.

Israel has already blocked two attempts by activists to deliver aid by ship to Gaza, in June and July.

The United Nations declared a state of famine in parts of Gaza, warning that 500,000 people face "catastrophic" conditions.