Quds city, July 18, SPA -- Some 20,000 police and soldiers were deploying in southern Israel on Monday to block a march of Gaza withdrawal opponents _ a crucial test run for security forces and protesters ahead of the August pullout. Organizers said marchers will try to reach the Jewish settlements in the Gaza Strip, even though police declared the demonstration illegal and last week barred nonresidents from entering the Gaza settlements. Settler leaders and police said they expected tens of thousands of participants Monday, in what could be the largest protest yet against the pullout. The crowd is to assemble in the southern Israeli town of Netivot, for the first leg of a three-day march to Gaza, 25 kilometers (15 miles) away. Some 12,000 police and 8,000 soldiers were being deployed throughout southern Israel to stop the crowd before it reaches Gaza, said police spokesman Avi Zelba. "It won't be easy," Zelba said. The marchers would be allowed to complete the first segment, of about 8 kilometers (5 miles), to the farming village of Kfar Maimon, a security official said, citing a preliminary police plan. The marchers would not be permitted to go on once they reach Kfar Maimon on Monday evening, the official said on condition of anonymity, because the work plan was still awaiting final approval. Monday's demonstration will test the resolve and ability of the security forces to deal with large numbers of protesters _ a situation troops will face again in mid-August when they begin removing 9,000 residents from their homes in 21 settlements in Gaza and four in the West Bank, according to a report of The Associated Press.