The Gaza-bound Global Sumud Flotilla (GSF) says a drone has struck its main ship in the Tunisian port of Sidi Bou Said, causing a fire, but that all its passengers and crew were safe.

A spokesman for the GSF blamed Israel for the incident, which occurred late on Monday, but the Tunisian National Guard said reports of a drone attack were “completely unfounded”.

The agency instead suggested that the fire was caused by a cigarette butt or a lighter setting a life jacket ablaze.

The GSF, however, insisted the incident was a drone attack and said it would provide more details on Tuesday morning.

There was no immediate comment from Israel.

The GSF comprises more than 50 boats, heading for Gaza to break the Israeli siege on the war-battered and famine-stricken Palestinian territory.

According to the GSF, the incident on the Family Boat, which is sailing under a Portuguese flag and carrying the group’s steering committee members, took place at 11:45pm on Monday. There were six people on the boat at the time of the drone attack, and some of the passengers quickly extinguished the fire.

All crew members are safe, it said in a statement.

The fire caused damage to the ship’s main deck and below-deck storage, it said.

The GSF posted multiple videos on social media that it said showed the moment the attack took place.

One video, taken from another vessel near the Family Boat, showed an incendiary device falling on the boat, causing an explosion. Another video, captured on the Family Boat’s security cameras, shows crew members looking up and jumping back before an explosion.