"Members of the public order police warned the demonstrators that the march was illegal and formed a human barrier to prevent the march from proceeding," Police Director Henriette Bester said in a statement, adding there were no injuries.

"I was personally very perturbed by the highly irresponsible behaviour of the demonstrators who involved children in this illegal march," she said.

Bester told Reuters that infants in pushchairs were in the march which had been banned under the Gatherings Act that requires prior notification of protests to the local authority.

About 10,000 extra police and troops are on duty in South Africa's economic capital for the World Summit on Sustainable Development (WSSD) that formally starts work yesterday and runs until September 4.

Uphill negotiations ahead of the U.N. summit resumed on the weekend in the tightly guarded Sandton conference centre between rich and poor nations to try to agree a blueprint to safeguard the planet.

DRAMATIC IMAGES

Dramatic television images fanned interest in Saturday night's confrontation between police and the anti-privatisation and pro-landless protesters.

U.N. officials were despondent that media coverage had been so rapidly dominated by the protest, following massive and violent demonstrations at previous international meetings in Seattle, Genoa, Prague and Davos.

"I hope that we start generating news here in terms of the environment. That's what will get people's attention," summit Secretary General Nitin Desai told Reuters.

"One has to accept that the media will pick what they want to pick in an open environment like this," he said.

Pessimism surrounds any prospects for major agreement at the summit after the last negotiating session had ended deadlocked in Bali in June.

Scant progress was made on Saturday, when rich countries expressed reluctance to grant new aid as part of a 77-page document meant to halve poverty in developing nations by fuelling environmentally friendly economic growth.

Delegates said compromises on issues including boosting healthcare, reining in pollution from burning fossil fuels and protecting dwindling fish stocks might have to await the arrival of an expected 100 world leaders for a two-day finale.

"It could go right to the end," one African delegate said.

"I think it's looking like we're going to get a pretty modest set of outcomes," said Tony Juniper, vice chairman of Friends of the Earth International. "It's clear that we're going to get no legally binding targets."

Environment and other ministers will lead formal talks starting yesterday after what is billed as a spectacular opening ceremony with African dancing and drumming on the weekend night.

Organisers say they expect up to 100 world leaders to attend - not including U.S. President George Bush. But they have slashed predictions for the number of delegates from 65,000 to about 40,000.

Johannesburg is a follow-up to the Earth Summit in Rio de Janeiro a decade ago that set goals for protecting the planet, ranging from curbing emissions of the polluting gases blamed for global warming to preventing the spread of deserts.