Ms Thunberg, who has rejected accusations she is antisemitic, replied soon after Mr Katz made his comments.

"As we are sailing closer to Gaza with Israel saying they will not allow the boat to arrive with humanitarian aid (which would be a crime by them), it's very important to keep in mind that this mission is not about us nor the boat," she posted on Instagram. "This is about the genocide, blockade and systematic oppression of Palestinians.

"People in Gaza don't need anyone to come and save them, they need us to amplify and support their struggle for justice, that we end our complicity, put pressure and cut ties with those committing human rights violations. Keep all eyes on deck but above all, all eyes on Palestine and all oppressed people."

Some of the campaigners on board the British-flagged "Madleen" which set sail from Italy last week, said Israeli forces were already trying to scramble their communications, including GPS signals.

"We know what that means, when they start jamming our communication, when they started messing with our devices, it means that they are preparing for an interception or an attack.

"And we all heard the Israeli media saying that they confirmed the unit S13 of IOF Special Forces, so they are preparing to commit a war crime, and we need to stop that."

Israel has repeatedly rejected allegations of war crimes in its conduct relating to the war in Gaza.

Israeli media has reported that the military plans to seize the ship and take it to the port of Ashdod, arresting and deporting the crew.