Israel's Katz said he instructed the military to "take whatever measures necessary" to stop the ship carrying Thunberg and other activists.

The attempt to block the flotilla carrying the famed climate activist comes 15 years after a similar aid effort ended in deadly violence.

Palestinian witnesses said Israeli forces had fired on them at a roundabout in the nearby city of Rafah as they went to get food from a site run by the Gaza Humanitarian Foundation (GHF). The Israeli military said it fired warning shots at people it said were suspects who had advanced toward its forces and ignored warnings to turn away.