Israel expelled 25 alleged pro-Palestinian activists who landed at its main airport on Friday and was interrogating another 30 suspects there, police told AFP.
"Twenty-five have been sent back where they came from," police spokeswoman Luba Samri said. "Thirty are still being questioned."
Organisers of the "Welcome to Palestine" campaign, which some have called the "flytilla," had said up to 800 activists were to fly in to Ben Gurion Airport near Tel Aviv, in a peaceful mission to visit Palestinian families.
But Israeli authorities said they largely managed to preempt the campaign by foreign activists -- most of them from France -- who are demonstrating for the right of access to the West Bank.
Officials said that by notifying foreign airlines of ticket-holders who would not be admitted to Israel they prevented hundreds from boarding at their ports of departure.