UN Secretary-General Ban Ki- moon on Thursday reiterated a call for the international community to combat desertification and land degradation.

"More than 1 billion poor and vulnerable people living in the world's drylands, where efforts to achieve the Millennium Development Goals (MDGs) face particular challenges and thus have lagged behind," Ban Ki-moon said in his message for the World Day to Combat Desertification and Drought, observed on June 17.

"The unremitting stress of drought, famine and deepening poverty threatens to create social strains, in turn creating the potential for involuntary migration, the breakdown of communities, political instability and armed conflict," he said.

Ban stressed the crucial role of drylands in maintaining biological diversity and productivity.

"Thirty percent of the crops that are cultivated and consumed in every corner of the world originate in drylands," the secretary- general said. "The biodiversity of dryland soil also plays a critical role in transforming atmospheric carbon into organic carbon -- the earth's largest pool of organic carbon.

Some 2 billion people depend on ecosystems in dry land areas, 90 percent of whom live in developing countries, according to a report of the UN Environment Program (UNEP).

Worldwide, more than 30 percent of the total land area is dry land. About 30 percent of dry lands are degraded, with particular susceptibility to desertification.

Globally, 20,000 to 50,000 square kilometers are lost annually through land degradation.