Earth summit must not fail - UN's Toepfer
"Johannesburg must be a precautionary peace conference. We are not allowed to fail," he told a news conference.
The World Summit on Sustainable Development starts on August 26 and runs to September 4.
It is expected to attract some 60,000 delegates including more than 100 heads of state and government who will be asked to agree and endorse action plans on water, energy, health, agriculture and biodiversity.
But even before the meeting starts, environmentalists have accused a group of nations led by the United States of blocking plans to set any targets and effectively emasculating a draft text on proposed actions.
Toepfer said the security of the world was at stake at the summit because the gap between rich and poor - north and south - had widened considerably in the decade since the first earth summit in Rio de Janeiro.
"That creates tensions and instability," he said, noting that even U.S. Secretary of State Colin Powell had accepted the connection between sustainable development and world security.