Israeli officials, citing fears of violent disturbances, on Monday deployed 20,000 police and soldiers to prevent hundreds of buses carrying opponents of Prime Minister Ariel Sharon's pullout plan from reaching staging areas in southern Israel.
The move stoked right-wing anger against Sharon, who has billed the withdrawal from occupied Gaza as "disengagement" from conflict with the Palestinians.
Sharon's plan is to remove all 21 settlements in Gaza and four of 120 enclaves in the West Bank starting in mid-August, Israel's first withdrawal from occupied land the Palestinians want for a state.
Looking for a showdown with Sharon, settler leaders had vowed to defy an official ban on their protest, which they had expected to attract more than 100,000 people.
It was to begin on Monday with a mass rally in the desert town of Netivot and end on Wednesday with a huge march to the crossing point to the Gush Katif settlement bloc.
But authorities feared clashes if protesters tried to break through the army's blockade of the settlements imposed last Wednesday.
"A decision was made to stop buses at the outset throughout the country all the way from the Golan Heights so that only a small number reach the south so we can ... minimise confrontation," police commander Amihai Shai said.
The YESHA settlers' council, which organised the protest, accused Sharon of "dictatorial tactics".
Sharon's plan is to remove all
21 settlements in Gaza
A settler spokeswoman said police held some buses before leaving and stopped others en route carrying protesters, though it was not immediately clear if any were turned around.
Israel Radio said bus drivers heading for pickup points were in some cases ordered to turn over keys and licences. Some protesters were turning to cars to circumvent the restrictions.
Settlers and their supporters have vented anger in the past by blocking highways and planting fake bombs in public places.
Polls show most Israelis support Sharon's plan, which international mediators see as a possible springboard to renewed peace talks.
About 8500 Jews live cloistered from 1.3 million Palestinians in Gaza.
Palestinians fear the plan will give them tiny, impoverished Gaza, while Israel strengthens its hold on much bigger West Bank settlements that house most of the 240,000 settlers.