As part of tight security preparations, South African authorities will declare a no-fly zone over the sprawling convention center where delegates will meet for a U.N. conference on racism, police said Tuesday.

No aircraft will be allowed to fly over a 0.62 square mile area above the convention center during the eight-day conference, which starts Friday in the coastal city of Durban, said police spokesman Bala Naidoo.

"We would rather take precautions," Naidoo said. "We are not taking any chances in this sort of thing."

More than 3,000 police officers from across the country have been called in to help maintain order at the conference, during which up to 50,000 protesters are expected to demonstrate a myriad of grievances.

Muslim demonstrators are seeking censure of Israel's treatment of the Palestinians. Descendants of African slaves are seeking reparations. Dalits, or "untouchables," on the lowest rungs of India's centuries-old caste hierarchy want their plight discussed.

About half of the security personnel will be protecting visiting dignitaries, including about 30 heads of state, Naidoo said.

The United States said Monday that Secretary of State Colin Powell had decided not to attend because of Arab-backed "offensive language" that accused Israel of implementing racist policies against Palestinians.

Police will patrol Durban's main roads with the assistance of army units, helicopters will take to the skies, and the South African air force will be on standby, Naidoo said.

Even underground, security will be tight. Storm water drainage systems will be monitored and man holes sealed off to block easy escape routes.

Recent world gatherings have been marred by protests that have turned violent.

Ben van Deventer, the conference's national security coordinator, said his office had been working closely with demonstration organizers to ensure the Durban protests are peaceful.

Security officials will have zero-tolerance for "trouble makers," Van Deventer said.

Meanwhile Tuesday, a watchdog group called on organizers to expel an Arab organization for distributing anti-Semitic pamphlets at a conference related to the U.N. conference on racism.

Pamphlets depicting Jews with fangs dripping with blood and wearing helmets inscribed with Nazi swastikas were distributed at a gathering of non-governmental organizations by the Arab Lawyers Group, said U.N. Watch official Andrew Srulevitch.

The NGO conference on racism is being held in advance of the U.N. gathering.

"Any NGO that is passing out hate literature at a world conference against racism should be kicked out," Srulevitch said.